Clay Sedimentation and Mineralogy in Drilling
Cores from the Sea of Japan
著者名(英)
Saburo AOKI, Norihiko KOHYAMA, Toshio ISHIZUKA
journal or
publication title
Journal of Toyo University. Natural science
number
52
page range
149-176
year
2008-03
URL
http://id.nii.ac.jp/1060/00002537/
Creative Commons : 表示 - 非営利 - 改変禁止
http://creativecommons.org/licenses/by-nc-nd/3.0/deed.ja
Journal of Toyo University， Natural Science， No．52：149－176（2008）
149
Clay Sedimentation and Mineralogy in Drilling Cores
from the Sea of Japan Saburo AOKI， Norihiko KOHYAMA and Toshio lSHlZUKAAbstract
The clay mineral assemblage and chemical characteristics of clay minerals in clay sediments were revealed by XRD and ATEM analyses of four drilling cores collected from the Sea of Japan． These results elucidate the paleoenvironments of the Sea of Japan and its surrounding land areas since the Neogene Tertiary． The four major clay minerals of smectite， chlorite， nlite， and kaoHnite are contained in aU of analyzed， except for the early and middle Miocene samples． A signi且cant amount of glauconite was identi且ed in clastic sediments of Quaternary and Pliocene using ATEM． Smectite concentrations increase markedly from the Quaternary to the early Miocene， whereas㎜te abundance shows an opposite trend． Chlorite concentration seems to increase concomitant with depth， but that is not as clear a tendency as that of smectite． Kaolinite contents revealed in this study were less than 10％， but they show an interesting trend not to contahl in early and middle Miocene samples and to increase toward Quaternary time． Chemical analyses of clay minerals show that smectite is classifiable into two垣）es：adi－octahedral as beidelHte and a tri－octahedral type as saponite． Chlorite is a tri－octahedral showing Fe－rich and FeMg－Al types． Chemical characteristics and respective morphologies of these clay minerals suggest that clay minerals in this study are of clas廿c origin， except fbr some smectite in Miocene tuff． Mineralogical and chemical analyses of clay minerals suggest that the Sea of Japan in the Miocene Tertiary received smectite rich sediments that originated from submarine and terrigenic volcanisms；they showed a decreasing tendency a丘er the Miocene and Pliocene． In Quaternary times， the tendency was reinforced and clastic clay minerals as illite， chlorite and kaolinite were supplied simultaneously仕om surrounding land areas by environmental changes of climatic cycles， denudation， river runoff， and weathe亘ng processes． On the other hand， on the Sea of Japan， submarine authigenic minerals such as glauconite and pyrite are fOrmed under reduction conditions in deel｝sea environments． Key words：ODP 127， Clay mineralogy and chemistry， Clay sedimentation， XRD， ATEM，Paleoenvironment
Natura1 Science Laboratory， Department of Economics， Toyo University 52＆20， Hakusan Bunkyou－ku Tokyo 112－8606， JapanIntroduction
Qualitative and quanthative estimations of clay minerals in surface sediments of the Sea of Japan were initiated by Aoki et al．（1974）． Oinuma and Aoki（1977）analyzed clay mineral compositions in seven piston cores from the Sea of Japan and discussed vertical variations in clay mineral compositions since the late Miocene． In 1987，0DP 127 drilled at four sites in the Sea of Japan：two sites were in the Yamato Basin（794 and 797）；site 795 was in the Japan Basin；site 796 was at the Okushiri Ridge． Figure l shows sites of the four drilling cores． Drilling cores at first three sites reached the basement rock basalt． The deepest at site is of the early Miocene；those of other three cores are middle Miocene． Many scientists from different disciplines have stUdied these drilling cores． Fegel et a1．（1990）discussed the relationship betWeen the clay mineral assemblage and 45°N 40°じ
130°E 135° 140° Fig 1． Location map showing ODP 127 dr皿ing sites in the Sea of Japan（from Tamaki， Pisciotto， Allan， et． A1．，1990）．Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan 151 REE in samples from sites 794，796， and 797． Of the ODP report， several authors have described clay minerals in drilling cores． Tada and Iijima（1992）described minerals in all samples studied here；those results are pertinent to the present stUdy． Nevertheless， as they reported， they were unable to describe minerals in detail． On the other hand， David et al．（1992）found di－octahedral smectite in altered volcanic glass of the Miocene blue tuff at sites 794 and 796． Boggs and Seyedolali（1992）pointed out that kaoIinite in sandstone at site 796 was formed through alteration of plagioclase． The present stUdy is intended to clarify the clay mineral composition and chemistry of clay minerals， with particular emphasis on factors influencing sedimentary processes since the Neogene Tertiary in the Sea of Japan．
Samples and analytica1 procedures
From drilling cores at four sites in this study，64 samples were selected． First， raw materials were softened in distilled water and then depickled． Clay fractions under 2 microns were collected through repeated sedimentation． Qualitative and quantitative estimations of clay minerals are based on methods reported by Sudo et al（1961）and Oinuma（1968）．Actual application of the methods is described in detail elsewhere（Aoki， S． et al．，1974；Aoki and Kohyama， N． 1998）． Analyses by XRD were performed under conditions of 40kV， 20mA， slit system 1－1－0．3°， CuKα， scanning speed l cm／min．， with a scanning range of 30°－3°． Chemical analyses of clay minerals were carried out using a transmission electron microscope（H8000；Hitachi Ltd）equipped with a solid・state detector for microcomputer fOr processing（Kohyama，1983）．Results
The analyzed samples showed the following clay minerals：smectite， chlorite， illite， and kaolinite． However， the contents of respective clay minerals differed among samples and among times． For example， samples at two sites from the Yamato Basin showed similar patterns in vertical variati皿s of the clay mineral compositions， as shown in Figs．2and 3． Those figures eXhibit increasing smectite abundance with depth， whereas illite concentration shows an opposite trend． Chlorite concentration does not show distinguishable features from the top to the bottom， but the highest concentration is present in the upper－most sample． Kaolinite is not contained in samples deeper than 252 m from the top of the core（upper Miocene）at site 797 and in samples deeper than 271 m from the top of the core（upper Miocence）at site 794． Samples at site 795 were collected from the northern Japan Basin． Figure 4 shows that the vertical change is clay mineral composition in samples at site 795 does not display a more evident pattern than those of the previous two sites． However， smectite abundance increases with depth， whereas illite shows an opposite trend． Vertical change in chlorite concentration is not systemtic． The kaolinite content is observed in samples shallower than 262 m deep from the top of the core（Pliocene）but it is not contained■smectite ■chlorite 口i‖ito ［コkaolinit● Fig 2． Vertica1 change in the clay mineral composition in drilling core at site 794． ■smect忙e ■chlorite 口illite 口kaolinite Fig 3． Vertical change in the clay mineral composition in drilling core at site 797．
Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan
153
5．98m 53．28m 1 1 O．28m 158．88m 224．88m 315．38m 483．98m 540．18m 598．18m 661．96m ■smectite ■chlorite 口illite 口kaolinite Fig 4． Vertica1 change in the clay mineral composition in drilling core at site 795． site 796 2．08m 2．98m 14．18m 50．18m 61．68m 110．53m 139．48m 180．98m 205．58m 263。78m 294．28m眺
20％ 40％ 60％ 80％ 100％ ■smectite 口chlorite 口iIlite 口kaolin民e Fig 5． Vertica1 change in the clay rnineral composition in drilling core at site 796．in older samples at site 796 from Okushiri r idge is shown in Fig．5． Contents of smectite and illite show similar patterns to those in previous sites， but vertical changes in the clay mineral composition at site 796 are less clear than at other three sites． Chlorite concentration do not show as distinguishable features as those at the other three sites． KaoHnite contents are not observed in samples older than 205 m dated PUocene． Analytical results obtained by ATEM show the following chemical compositions and figures of clay minerals． In samples from site 794， a Quaternary sample of 23．78 m layer contained numerotls glauconite－like minerals that have high iron and potassium contents． Morphology of the mineral shows that it is pillared and irregular． A TEM figure and a Iist of its chemical composition are shown in Fig．6and Table 1． The late Miocene sample of 306．28 mdeep contains many smectite particles that belongs to beidellite and tri－octahedral saponite． Beidellite is ro皿d and irregularly shaped． A TEM figure and chemical composhion are also shown respectively in Fig．6and Table 1． The middle Miocene sample of 468．58 m deep shows prevalent smectite and illite． Smectite is entirely beidellite；it is round and pillared． Its TEM images and chemical composition are shown in Fig．7and Table 2． A． Quaternary sample from 9．38 m deep at site 797 in the Yamato Basin comprises smectite， illite， and glauconite． The TEM morphology and chemical composition of these clay millerals are shown in Fig．8and Table 3． Morphology and the outline of smectite are not clear． Smectite belongs to Al－beidelHte． Glauconite is round or irregularly shaped． The morphology of illite is irregular but the outline is sharp． A PIiocene sample of 135．33 m deep contains smectite， illite， and glauconite． Morphology and chemical compositions of clay minerals are also shown in Fig．8and Table 3．「lhe morphology of beideMte is partly cloudy and not clear． Illite is irregularly shaped， but clear cut． In contrast， the surface pattern of glauconite is recognized， but it is unclear and irregular． Figure 9 and Table 4 show a Pliocene sample of 191．48mdeep， showing the preseIlce of田ite and smectite． Smectite is beidellite like fleecy clouds． The middle Miocene sample of 369．94 m deep contains much smectite． The TEM figure and chemical composition of smectite are also shown in Fig．9and Table 4． The morphology of smectite differs greatly among samples． In addition， its chemical composition suggests it to be beidellite from Al－type to Fe－Mg type． The early Miocene sample of 524．98 mdeep has abundant smectite． lt is round， but the outline is not clear， showing characteristics of smectite． They are all beidellite， as shown in Fig．9and Table 4． A Quaternary sample of 5．98 m at site 795 from the Japan Basin shows prevalent smectite and illite． Its TEM morphology and chemical composition of clay minerals are shown in Fig．10 and Table 5． Smectite is Al－type． Imte has potassium ion of O．50 to O．40 in the interlayer． This smectite is pillared， like illite．111ite appears as a long strip of paper or square shape． A PIiocene sample from 110．28 m depth has saponite and chlorite． Its morphology and chemical composition are shown respectively in Fig．10 and Table 5． Saponite is pillared and chlorite is short－pillared． Pliocene sample from 187．58 m depth contains abundant smectite． The triangular material is beidellite and the pillared one is chlorite． The petal－shaped material is
Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan
155
Al－beide田te． Chlorite is the pillared shape． Its TEM morpholohgy and chemical composition are shown in Fig．11 and Table 6． A middle Miocene sample from 661．96 m depth contains smectite and illite． The morphology of smectite shows typical shape like that of fleecy clouds． Smectite is all beidellite． mite shows an irregular pattern． Its TEM morphology and chemical composition are also shown respectively in Fig．11 and Table 6． A Quaternary sample of 2．08 mdeep at site 796 in the Okushiri Ridge contains illite and glauconite』hte is piUared and glauconite is short pillared or irregtilarly shaped． Its TEM image and chemical composition are shown in Fig．12 and Table 7． A Pliocene sample of 61．68 m deep contains much smectite that is beidellite． Morphology is a clear quadrangle． Its TEM figure and chemical composition are also shown in Fig．12 and Table 7． The upper Miocene sample of 263．78 m deep has smectite and chlorite． Its TEM figure and chemical composition are shown in Fig． 13and Table 8． Smectite is all beidellite． The outline is not clear because it has fleecy clouds like smectite． The upper Miocene sample of 294．28 m deep is rich in smectite． Its TEM morphology and chemical compositi皿are also shown in Fig．13 and Table 8．”1 he outlme is cloudy；it is not clear． Smectite belongs to Fe－type and Al－type．Discussion
Clay mineral composition and chemical characteristics of clay minerals were analyzed in samples from four drilling sites from the Yamato Basin， Japan Basin， and Okushiri kidge in the Sea of Japan． Clay minerals such as smectite， chlorite， i田te， and kaolinite were identified and quantified． Table 9 shows average contents of respective clay minerals in ildividual geological time to show overall characteristics of the clay mineral compositions in samples from the fOur sites． That table shows that smectite abundance tends to decrease廿om the early Miocene， Pliocene toward Quaternary times， whereas illite abundance exhibits an opposite trend． Kaohnite contents are not observed hl samples older than upper Miocene at two sites of the Yamato Basin and in samples older than PHocene at sites of the Japan Basin and Okushiri Ridge． On the other hand， chlorite concentration shows a slight decreasing trend toward yo皿ger geological age， although it remains less clear than that of smectite concentration． Figure 14 shows a sedimentary columnar section of each core． In Quaternary time， clastic clay mineral such as chlorite and illite， which comprise 7460％of the total clay mineral assemblage， were transported to the Sea of Japan． On the other hand， the smectite content of Quaternary time sediments was 27－15％． Smectite concentration， however， is high in the Pliocene time because volcanic materials are contained in clastic sediments． For example， in a Pliocene sample of 5060 m deep at site 796 from the Okushiri r idge， smectite concentration increases more than 40％． This increase might be attributed to the input of volcanic sand to the sedimentary layer． In early Pliocene and upper Miocene times， the smectite contents vary from 60％to 30％in accordance to volcanic influence． In a sample at site 796 from Okushiri Ridge，clastic sediments of clay and silt size exist in more half of the samples of the Pliocene time， whereas Pliocene samples of other sites are largely composed襲
讐
轟
Fig 6．、A
●、
ぷ藩ぶ
D
TEM morphology of glallconite and smectites in samples of the Quaternary and upper Miocene at site 794． Bar is l micron．Clay Sedimentation and Mineralogy in Driding Cores from the Sea of Japan
157
Table 1．Sio2
AI203
MgO
F●203（F●O）MnO
Tio2
CaO
Na20
K20
Totel（％） SiAl
Tetra．Al
Mg
Fe3（Fo2）Mn
Ti
Octa．Ca
Na
K
Inter．794－A 794－B 794－C
giaUCOnite g leUCOnite SrneCtite 57．12％ 17．98％ 1．85％ 15．41％ 0．29％ 1．18S6 0．38％ O．9016 4．89％ 1 OO．OO％ 3．64％ 036％ 4．00％ O．99％ 0．18％ O．74％ α02％ O．06％ 1．99％ O．03％ O．11％ 0．40％ 0．54％ 50．83 19．92 2．67 16．55 0．61 1．21 0．81 2．02 5．38 100．0096 3．33 0．67 4 0．87 0．26 0．81 0．03 0．06 2．06 0．06 0．26 0．45 0．77 63．65 20．42 4．32 6．2 0．77 0．21 0．88 0．89 2．65 100．00％ 3．86 0，14 4 1．32 0．39 0．28 0．04 0．01 2．04 0．06 0．11 0．21 0．38794－D
saponite
56．2 14．85 12．47 （1・4．36） 0．29 0．11 0．34 0．36 1．02 100．ooe6 3．61 0．39 4 0．74 1．2 （0．77） 0．02 0。01 2．74 0．02 0．04 0．08 0．14 Chemical composition and g． tructural formulae of g正auconite and smectites in samples of the Quaternary and upper Miocene at slte 794． TEM morphology of each clay mineral is shown in Fig．6．於
B
ぺ
儀 蕪難，
Fig 7． 巾紗 鷲∨繋
TEM morphology of slnectite and illite in samples ofthe middle Miocelle at site 794． Bar is l micronClay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan
159
Table 2． 794－A 794－B smect辻e ill忙e Sio2 60．28％ 48．91 Al203 14．04％ 27．83 MgO 8．92％ 4．61 F●203（F●0） 9．82％ 4．14MnO O．53％ t42
Tio2 0．75％ 1．33 CaO 1．06％ 1．06 N820 0．00θ6 1．95 K20 4．61％ 8．75 To匂1（％） 100．00％ 100．00％ Si 3．78％ 3．16 Al O．22％ α84 Tetra． 4．00％ 4 Al O．8296 1．27 Mg O．83％ 0．44 Fe3（Fe2） 0．46％ 0．2 Mn O．03％ 0．08 Ti o．04％ 0，06 0cta． 2．18％ 205 Ca O．0796 0．07 Na O．00％ 0．24KO．37960．72
1nter． 0．44％ 1．03794－C
il慌e 47．79 33．46 3．4 3．65 0．46 0．57 0．21 0 10．46 100．oo！6 3．06 0．94 4 1．58 0．32 0，18 0．03 0．03 2．14 0．01 0 0．85 0．86 Chemical composition and strucutaral formulae of smectite and illite in samples of the middle Miocene at site 794． TEM morphology of each clay rnineral is shown in Fig．7．漸
A
C
醒
嵯 彰 ×D
蘇 馨 さ牛 Fig 8． TEM morphology〔）f smeclites， glauconi亡e， alld illite ill saml）les of tlle Qua亡ernary and Pliocene at site 797， Bar is l miCrOI1．Clay Sedimentation and Mineralogy in Dri 797－A 797－B 88ponite d8UC◎n忙e Table 3．
Sio2
AI203
MgO
F●203（F●O）MnO
Tio2
CaO
Na20
K20
Total（％） SiAl
Tetra．At
Mg
Fe3（Fe2）Mn
Ti
Octa．Ca
Na
K
Inter． 55．06％ 17．27S6 5．38％ 〈14．em） O．68％ 0．99％ 1．41％ 1．03％ 3．28％ 100．00％ 3．52％ O．48％ 4．00％ 1．3（”S O．51％ （0．72％） 0．04％ O．05％ 2．62％ 0．10× 0．13％ 0．27％ 0．50％ lling Cores from the Sea ofJapan 51．42 20．05 4．96 13．01 1．Ol 1．74 1．33 1．37 5．11 100．00％ 3．33 0．67 4 0．86 0．48 0．63 0．06 0．08 2．11 0．09 0．17 0．42 0．68 797－・C i旗e 55．5 22．49 3．04 3．47 1．72 1．62 0．93 1．63 9．6 100．0096 3．55 0．45 4 1．24 0．29 0．17 0．09 0．08 1．87 0．06 0．2 0．78 1．04797－D
smectite
47．3 26．44 3．08 9．23 3．36 3．07 2．25 3．27 2 1 OO．OOS6 3．05 0．95 4 1．06 0．3 0．45 0．18 0．15 2．14 0．16 0．41 0．16 0．73 161 Chemical composition and structUral formulae of smectites， glauconite， and illite in samples of the Quaternary and Pliocene at site 797． TEM morphology of each clay mineral is shown in Fig．8．賀
sueeSt，ぞ 、
．ジ 〉 蓋濠
Fig 9． TEM molphology of smectitc and illite in samples〈）fthe Pliocene and ear】y Miocelle at site 797， Bar is l IniCrOI1，Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan
163
Sio2
Al203
MgO
F●203（F●0）MnO
Tio2
CaO
Na20
K20
Total（％） SiAl
Tetra．Al
Mg
Fe3（Fo2）Mn
Ti
Octa．C8
Na
K
Inter．797－A
illite 51．66％ 20．41％ 3．79％ 4．93％ 3．97％ 3．52％ 1．94％ 6．66％ 6．66％ 100．00％ 3．37％ 0．63％ 4．00％ 0．94％ 0．37％ O．24％ 0．22％ O．1 7％ 1．94％ 0．14％ 0．40％ 0．55％ 1．09％797－B 797－C
smed諏
60．57 11．79 5．34 9．5 2．3 2．67 2．24 2．66 2．93 100．00％ 3．84 0．16 4 0．72 0．5 0．45 0．12 0．13 182 0．15 0．33 0．24 0．72 797－D smectitE S「nect辻e 51．15 16．06 5．25 6．95 3．96 3．69 4．99 4．66 3．29 1 OO．0096 3．36 0．64 4 0．61 0．51 0．34 0．22 0，18 1．86 0．35 0．59 0．28 1．22 54．4 10．23 4．13 19．98 1．87 1．59 4．26 2．03 1．51 100．00％ 3．58 0．42 4 0．37 0．41099
0．1 0．08 1 ．95 0．3 0．26 0．13 0．69 Table 4． Chemical composition and structUral formulae of smectite and i田te in samples of the Pliocene and early Miocene at site 797， TEM morphology of each clay minera1 is shown in Fig．9．C κ 七S ぐ 然 w叉ぐ こ ㊤ で
擬灘、
講蕪
濡 × 熟 c 〔 S 警÷ 滋蘂蘂
る …一 彫Cぐ ご 撫㎏研 ぷ wo※A － s － ℃ 蕪： 一 （ ぐ ℃ ∨ ◇懲 ざ 三 ◇〉 S … ㎏ 渠 ……三
…． ﾘ三 … ぎza ㌘ 鷲彰葺
稔ぺ ぱ ※ ㎏＿
鍵鐸 uet 蕩⊆鷲一毯慈 es一 ご叉㍍ fi一愁黙変陣 悲ジ三ぐ○ 菜 叉 」 Cぐ × 〔 言一…派懇 … 珍烹 馨 竺 …ぎ こ麓
≡蓑葦 ≡
鱒
戸繰 ＿頴無搭∀ 難i難 織彩蔭難難
彩簸渓ごwn灘診 慾亥轟
ぶ汚 ㌘s彩藤
mmt ぺ｝．蕪
羅
縢
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＝塾
叉 上 ス叉 融 き濠 慾ミ論
蘂、 蓉総 ” 頴 変ざ這懸
℃ ※ ぎ 照熈 壕 ◇x と叉礎灘難
烹…難
諜
覇
漁鷲購ぶ ジ三響
購琵轟獣
TEM morphology of smectites， illite， and chlorite in sarnples of the Quaternary and Pliocene at site 795Bar is l mcron Fig 10．Clay Sedimentation and Mineralogy in Drilling Cores from the Sea ofJapan
165
Sio2
A1203
MgO
F●203（F●O）MnO
Tio2
CaO
Na20
K20
Tota1（％） SiAI
Tetra．AI
Mg
Fe3（Fe2）Mn
Octa．Ca
Na
K
Inter．795－A
srnectite
50．31％ 21．05％ 3．83％ 8．40％ 2．97％ 3．03％ 1．78％ 4．45％ 4．18％ 100．00％ 3．27％ O．73％ 4．00％ 0．89％ 0．37％ 0．41％ 0．16％ O．15％ 1．98％ 0．12％ 0．56％ 0．35％ 1．03％795－B
illito 54．07 21．4 2．93 7．15 2 2．2 1．23 292 6．1 1 OO．0096 3．47 0．53 4 1．09 0．28 0．35 0．11 0．11 1．94 0．08 036 0．5 0．94795－C
s8pon比e
50．88 9．78 14．61 （18．15） 11．2 0．27 1．43 1．47 1．29 1 OO、OOS6 3．33 0．67 4 0．09 1．43 （0．89） 0．06 0．06 2．53 0．1 0．19 0，11 0．4795－D
chlo疏e
38．47 21．02 1 2．69 ｛22・52り 092 0．96 0．78 0．71 1．93 1 OO．OOS6 3．43 0．57 4 1．64 1．69 （1．68） O．07 0．06 5．14 Table 5． Chemical composition and structural fbrmulae of smectites， illite， and chlorite in samples of the Quaternary and Pliocene at site 795． TEM morphology of each clay mineral is shown in Fig．10．ぺ 馨 Pビ
A
C
一濠D
FigIL
TEM morphology of smectite， chlorite， and il｜ite in samples（）f the Pliocene alld middle Miocene at site 795． Bar is l micr〔m．Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan
167
Sio2
Al203
MgO
F●203（F●O）MnO
Tio2
CaO
Na20
K20
Total（％） SiAl
Tetra．Al
Mg
Fe3（Fe2）Mn
Ti
Octa．Ca
Na
K
Inter．795－A
smectite
61．42％ 1 3．30S6 5．60％ 14．95％ 0．46％ O．54％ 1．15％ O．ooe6 2．58％ 1 OO．OO％ 3．85％ 0．15％ 4．00％ 0．83S6 0．52％ O．70％ 0．02％ O．03S6 2．10％ 0．08％ 0．00％ 0．21％ O．29％795－B 795－C 795－D
chloritg smect辻∈ il阯e
37．04 66．36 50．73 20．23 18．91 25．3 64 203 1．78 （33．47） 5．86 8．8 0．97 0．9 0．72 0．42 0．95 2．04 0．37 2．23 0．43 0．61 1．05 0．68 0．49 1．71 9．52 100．00％ 1 OO．em 100．00％ 3．46 4 3．29 0．54 0 0．71 4 4 4 t68 134 1．22 0．89 0．18 0．17 （2．61） 027 0．43 0．08 0．05 0．04 0．03 0．04 0 5．29 1．88 1，96 0．14 0．03 0．12 0．09 0．13 0．79 α39 0．91 Table 6． Chemical composition and structural formulae of smectite， chlorite， and illite in samples of the Pliocene and middle Miocene at site 795． TEM morphology of each clay mineral is shown in Fig．11．答 ．ご 灘疑 ぷ、逢、
B
漏
糠ジ
囁胃 ，’ 「内~内 よ． ’怠C
D
「芯 慾「 鷺㌘ ⊆ “ 《 ㊧． 「該で ∨＝ “ ’tP 、． 簿懸Fl憲蕉薫鞘轟嚢灘灘嚢臨 蟻叢醸蕪」轟琴灘『、
Fig l2． TEM morphology ofglaucollite、 illite， and g． nlectite in samples onhe Quaternary and Plioeene at s▲te 796． Bar is l micron．Clay Sedimentation and Mineralogy in Drilling Cores from the Sea ofJapan Table 7．
Sio2
At203
MgO
F●203（FoO）MnO
Tio2
CaO
Ne20
K20
Totd㈲
SiAl
Tetra．Al
Mg
Fe3（Fe2）Mn
Ti
Octa．Ce
Na
K
Inter．796－A 796－B
glauconite g lauconite 59．57％ 13．49％ 0．00％ 19、17％ 0．24％ 0．00％ 0．66％ O．OOS6 6．87％ 1 OO．OOS6 3．86％ 0．14％ 4．00％ 0．89S6 0．00％ O．93％ 0．01％ O．OOS 1．83％ 0．05％ O．OO％ 0．57S6 0．62％ 51．39 27．96 0．59 11．31 0．84 1．32 0．73 0．6 5．25 1 OO．OO％ 3．26 0．74 4 1．35 0．06 α54 0．05 0．06 2．06 0．05 0．07 0．42 0．54796－C
itlite 48．56 31．88 1．38 2．43 1．75 1．5 0．85 1．66 9．95 100．0096 3．12 0．88 4 1．54 0，13 0．12 0．1 0．07 1．96 0．06 0．2．1 0．82 1．09796－D
㎝ectit6
53 13．39 3．91 19．15 1．4 2．08 1．96 221 2．9 100．OC”6 3．48 0．52 4 0．52 0．38 0．95 0．08 0．1 2．03 0．14 0．28 0．24 0．66169
Chemical composition and structural formulae of glauconite， illite， and smectite in sampleg． of the Quatternary and Pliocene at site 796． TEM morphology of each clay mineral is shown in Fig．12ス内 遁
襲
パ㌻， ※罵 C購
㌢ ㌘A
曽や ’C
D
㌫灘
／／t ’ Fig 13． TEM nloq）11010gy（）f smcctite alld chlorite iii saml）les of the uppel’Mi（）cene at site 796． 11〕icrOn， Bar is 1Clay Sedimentation and Mineralogy in Drilling Cores from the Sea of Japan 171 Table 8．
Sio2
Al203
MgO
F●203（F●O）MnO
Tio2
CaO
N820
K20
Total㈲
SiAl
Te廿a．Al
Mg
Fo3（Fe2）Mn
Ti
Octa．C8
Na
K
Inter．796－A
srnectite
58．22％ 18．57％ 4．01％ 11．98S6 0．80％ 1．22％ 1．64％ 1．05％ 2．51％ 1 OO．OOS6 3．65％ O．35％ 4．00％ 1．02％ 0．37％ 0．56％ 0．04％ 0．06％ 2．05％ 0．11％ 0．13％ 0．20％ 0．44％796－B
sm●ctite
62．59 1 3．47 3．52 15．37 0．48 0．56 0．6 0．84 2．57 100．0096 3．91 0．09 4 0．9 0．33 0．72 0．03 0．03 2．Ol O．04 0．1 0．21 0．35796－C
chlorite
37．99 18．32 9．78 （・30．08） 0．73 0．83 0．62 0 1．65 1 OO．0096 3．51 0．49 4 1．5 1．35 （2．32） 0．06 0．06 5．29796－D
smectite
66．62 14．16 4．02 8．84 0．37 0．95 1．61 0．86 2．57 1 OO．0096 4 0 4 1．02 0．37 0．41 0．02 0．04 1．86 0．11 0．1 0．2 0．41 Chemical composition and structural formulae of smectite and chlorite in samples of the upper Miocene at site 796． TEM morphology of each clay mineral is shown in Fig．13．of diatom ooze． The contents of i－te and chlorite Pliocene ooze sediments vary from 57％to 54％．EVidently， they decrease in comparison to Quaternary clastic sediments． On the other hand， smectite concentration increases up to 43％． The lower half of the Pliocene sample at site 795 comprises diatom clay， which develops in upper Miocene samples at other sites and continues to sMceous， calcareous， and phosphorous clays in the middle Miocene． Figure 14 illus廿ates that血ese samples partly contain tuff materials． The contents of iMte plus chlorite in the late Miocene decrease from 51％to 44％， whereas the smectite concentration increases 廿om 46％to 52％． In the middle Miocene， illite plus chlorite concentrations decrease from 43％to 25％， whereas smectite increases from 57％to 75％． In the early Miocene， as shown in the sample at site 797 the content of illite plus chlorite is 33％；that of smectite is 67％． The authors examined the relationships between clay mineral compositions， sediment types and geological ages． We point out that clastic clay sediments in Quaternary 6me are composed largely of illite and chlorite derived from weathering products and smectite originated丘om volcanic materials． In the Neogene］［＞rtiary sediments tend remarkably to contain biological materials and have decreased contents of clastic clay minerals from the Pliocene to Miocene． Instead， smectite concentrations increase． Increasing smectite concentrations seem to be related closely to the presence of volcanic materials in the Miocene time． Four drilling cores contain more or less volcanic material derived from subma血e and terrigenous volcanism， th皿gh it differs With time and space in the Neogene Teriary． Blue tuff that originated from such volcanism was discovered by shipboard scientists， along with altered di－octahedral smectite． The major cause of the highest concentration of smectite in the Miocene is at垣buted to the wide occurrence of submarine and terrigenous voicanism． Tada and珂ima（1992）described bentonite tuff at site 794（middle Miocene）and site 797（late Miocene）and considered that the tuff was pyroclastic flow sediment． Barnes et al．（1992）reported that the blue tuff at site 794B（14．9M）was formed Quarter． Plio． U．Mio． M．Mio． L．Mio． Querter． Plio． u．Mio． M．Mio． L．Mio．
S
15％ 33× 52％sn
67％S
26％ 43％ 51％ 59％ 797（Yamato Basin）C
22％ 1 9S6 12％ 17％ 15％ 795（Japen Basin）C
25％ 19％ 1 O）S 14％ 1 52％ 38％ 32％ 26％ 18％ 1 36％ 35％3眺
27％％
K1
1
眺眺眺眺
1K銚銚仇眺 1
S
20％ 31× 46％75X
S
27× 37％ 49％ 794（Yamato Basin） C I 23％ 41％ 16S 37％ 18％ 30％ 眺 16X 794（Okujiri Basin） C I 14％ 46％ 20％ 34％ 15％ 36％K
16％ 1 6S6 6％K
1 3S6 9％脇
Table 9． Average contents of respective clay minerals in individual geological d㎞e． Quarter：Quaternary， Plio：Pliocene， U． Mio；upper Miocene， M． Mio middle Miocene， L Mio：10wer Miocene， S： smectite， C：chlo亘te，1：illite， K：kaoliniteClay Sedimentation and Mineralogy in Drilling Cores from the Sea ofJapan
173
SITE 797 （Yamato Basln｝ WD＝2862 m SITE 794 （Yam8to B日81n｝ WD＝ 281 1 m S｜TE 795 （JEpan Basln｝ WD ． 3300 m SITE 796 （Okushlrl Rldge） WD ． 2571 m 0 100 一 ・ 一● 一 ． 一 ． 一 ． 一 ∈Φ冠コO 200 ΦにΦOO＝吐 300 400 500 600 700 800 900 ー・田（（・「占・． －．．、・ △△△△△ ▲▲▲▲▲△ △△△▲△△ △△△△△△ △▲▲△』」△ △△▲』」△△ △写」z」▲△▲ △△△ぬL△△ △△△4」▲△ ×÷÷÷÷÷÷“や 〃〃多φ〃〃〃〃 Φ⊂Φ8亘」8｝ Φ⊂ΦOO一〜’，「⊂ ？ 》∨》》》∨ 》》∨》》》 ∨》》》》∨ 》》》∨∨》 ミ“《A《．、こ．、こ．、こ♪《． 》》∨》》∨ 》∨∨》》》 ．．、 ・、 ．．、 ・、 ．．、 ．㍉（ ．．、 ．㌔“ ．苛、 シ＾ ．．、 ．㍉、 ．．、 ■、p ．、㌔ ．、． 、 ．、■ 、． ．、． 、 ．、． 、 ．、． ■、． ∨VV》V》 》》》》》》 1’：：・：：買：t’1：、二：t’：：lt i翰：1ご：i÷：iぶ膏 跡玲、・1・i・：li・r・i・＞s・ 》∨》∨》》 》》》V∨∨ ∨》》V》》 Φ⊂ΦOO一Σ」Φ」50一 T．D．903 mbst A B Cl 一 一 一 C2 ▲△▲△△△ △△△△△△ △△△△△△A‥AAA△
』L▲△△△△ △▲△△△△ △▲▲△△△ △△△▲△△ △△▲▲△△ ．罵コO ρ庄 D Φ⊆80茎」aα⊃ E 、多（stl〈s 、t－mN－tNN 、ftsNtl“ 、’■qNf■〈N 、〃、lt、 》》》∨》》 ∨∨》》》》 》∨∨》》∨ 》》》》》》 》∨》》》》 Φ⊂Φ8一ΣΦ一這E TD．654 mbst A ⑩E巴mコON
B C1N
ΦCOOO＝江 C2 DN
△△△△△ AAA」△△ △△△△△ △△△▲△ △△△△△ △▲▲△△ △△▲△△ △△△△△ △△△△△ △△△△A △△‥△△ △AA△▲ △△△△△ △△△△△ △△△△△ △△△△△ △▲△△△ Φ⊂8。茎」§⊃ E 、ン、ノ、’、 ∨》v》∨》 ∨》》∨》∨ V∨》》V》 ∨》》》》》 》∨∨V》》 Y∨》∨∨∨ VV∨》》》 Φ⊂ΦOQΣΦ6豆E T．D 762 rnbsf 1 A B ！ Cl ！C ！！ C2 ．、P’・、． ．一．一．一．一， ’ 、’ ．一．一’一．一 ．、．ろ、． ．一．一．一・一． ’ 、’ ．一．一．一，一 ．、．’．、． ．一．一．一，一． ’ 、 ’ ．一・ 一層 一 ． 一 ．、：’＼： ’．、’D ．、層’、、． ク Nチ ．、：’♪： ’．、’． ．、〆“． ご シび ，・：’．・： ’．、’C P、．’．、・ ’．’ ，罵コO ，（，、°’♪，、 、’、’、’、’ ’、’、’、’〉 Φ⊂ΦOO＝江 4L△△ ，b」△▲△ △△△▲△ △△△△△ sN －1、11 Φ⊆Φ8逐」8合 ．〆・ン・♂・’・♂．♂ 、・、．S・、．、・、・ ・’・’・’．♂・才・’ ㌔” ttNxtl tt tl Φ⊂8旦Σ，E D T．D．465 mbst Seatloor ？・ Clav and stlty day Cb8rt arUt sMceous cSar altθmaOen phosPt旧口ccley D已lo而daγ ．、、，、、♪《ttc．、、． p；バ㌻ゾペ㌻ ミ、c㌻、ぶぺ’ AdiaQL－anataay Vdcanlc sand Bloda5lic sand “NS ssミI NS ÷㌔ヘベ㌔φ “t－÷〈t“tl÷－t“ft “べ㌔べ”〉” P8bb厚 claystone 》∨》》》 》》∨∨∨ 》》》∨∨ Fig l4． Stratigraphy at Leg 127 drill sites（froln Tamaki， Pisciotto，Allan， et al．，1990）．under a great scale of submarine magmatism and is composed almost entirely of regenerated hydroclastic glass． The blue tuff of site 796B（7．6M）was fOrmed under shallower submarine magmatic eruption． Barnes et al． discuss the co－relation of blue tuff in the Yamato Basm and Japan Basin， which sedimented in deep or deeper basin by gravitational flow． In Pliocene tilne， the supply of volcanic materials to the Sea of Japan con廿nued， but not to the extent of that during the Miocene． Therefbre， the abundance of smectite decreased． In Quaternary time， clastic materials were supplied from surrounding lands to that area because of env加nmental changes such as weathering， denudation， and sea－level fluctuation． Results show that clays and silt， which are largely composed of illite and chlorite， have been prevalent in Quaternary sediments． Another characteristic of Quaternary sediments in this study is the presence of glauconite， which is iron－rich micaceous mineraL GIauconite is wen known to be an authigenic mineral formed under the reducing conditions in marine environments． Follmi and Breymann（1992）reported the occurrence of glauconite in Pliocene and Miocene samples at sites 798 and 799． In addition， Kobayashi and Nomura（1974）fbund the occurrence of pyrite in the lower half of a piston core collected from deepsea floor of the Sea of Japan． These facts suggest that the deel｝sea floor of the Sea of Japan is situated in a reducing environment that readily fOrms such iron－rich minerals as glauconite and pyrite． Regarding chemical compositions of clay minerals， smectite ident近ed as di－octahedral beidellite was contained in all samples． Half of the beidellite is an aluminous type；the remainder is Al－Fe or Fe－Al type． A tri－octahedral saponite is FeMg type， but that saponite is not contained much in the studied samples， judging from the morphology of smectites， which are of clastic origin． The morphology of authigenic smectites shows hair－hke and fleecy cloudy materials， which are not recognized in these observed samples． On the other hand， di－octahedral montmorillonite contained in the blue tuff of the middle Miocene time has such morphological characteristics（Aoki， S． et al．， to be pubhshed）．Chlorite in this study belongs to a tri－octahedral Fe，Al－Mg type． The respective morphologies of smectite， chlorite， and i皿te in this stUdy imply their clastic origin． The kaolinite contents revealed in this study are the smallest component of the fOur clay mineral assemblage；they increase after the Pliocene． Lesser amount of kaolinite， or its absence， in the Miocene time might be attributable to the dilution effect by high concentrations of smectite and intermediate amounts of illite and chlorite． Kaolinite formation is well known to be sensitive to enVironmenta1 changes． For example， kaolinite is formed by chemical weathering in lower latitude land areas． Accordingly， the kaolinite contents in drilled cores from the Sea of Japan might suggest control by environmental changes in the Sea of Japan surrounding land areas． A small amount of kaolinite， however， might not be a strong indicator to paleo－environmental factors． Siliceous and calacareous ooze of biological origin prevailed throughout the Miocene time， but tuff and volcanic partly intercalated in the sediments． High concentrations of smectite in
Clay Sedimentation and Mineralogy i 1 Drilling Cores from the Sea ofJapan
175
the Miocene time are attributed to these volcanic materials． Clastic clay minerals such as illite and chlorite tend to increase toward the late Miocene from the early Miocene time， whereas smectite abundance showed…an opposite trend． Kaolinite was almost undetected in samples of the Miocene time． Oinuma and Aoki（1977）observed clay mineral compositions of seven piston cores from the Sea of Japan and pointed out that smectite concentrations decreased toward the Holocene， whereas the illite contents increased toward the uppermost areas of the cores． The chlorite contents in the tWo cores decreased remarkably in the lowest of the cores in the Pliocene time． They concluded that the cause of vertical change in the clay mineral composition was attributed to weathering and denudation land areas by paleoenvironmental changes． This stUdy fUndamentally supports those precedent results．AcknowledgementS
The authors thank Emeritus Professor K Oinuma of Toyo University fOr his continuing gtiidance and Professor K Tamaki of the University of Tokyo for supplying drilling cores for this study．References
Aoki， S．， Oinuma， K． and Sudo，T（1974）The distribution of clay minerals in the Recent Sediments of the Japan Sea． Deep－Sea Res．，21：865875， Aoki， S． and Kohyama， N．（1998）Cenozoic sedimentation and clay mineralogy in the Northern part of the Magellan Trough， Central PacMc Basin． Mar． Geol．，148， 21－37． Barnes， D．B． and Rene， P（1992）Sedimentology， phenocryst chemistry， and Age－Miocene “blue tuff’：sites 794 and 796， Japan Sea． Proc． ODR 127／128：115130． Fagel， N．， Andre， L．，Chamley， H．， Debrabant， P and Jolivet， L．（1990）Clay Sedimentation in the Japan Sea since the Early Miocene：influence of source－rock And hydrotherma1 actiVity． Sediment． Geol．，80：27－40． Follmi， KB． and Breymann， M．V．（1992）Phosphates and glauconites of site 798 and 799． Proc． ODP，127／128：63－74． Kobayashi， K． and Nomura， M．（1974）Ferromagnetic minerals in the sediment Cores collected from the Pacific Basin． J． Geophys．，40：501－512． Kohyama， N．（1983）Evaluation of airborne asbestos fibers by mans of electron Microscopy． Rept． Nat． indust． Health， FY 1981－1983，105：1－16．（in Japanese） Oinuma， K（1968）Method of quantitative esimation of clay minerals in sediments by X－ray diffraction analysis． J． Toyo Univ．， Gen． Educ．，10：1－15． Oinuma， K and Aoki， S．（1977）The vertical variations in the clay mineral compositions of the sediment core samples from the Japan Sea． J． Toyo Univ．， Gen． Educ．，20：1－16． Sudo， T， Oinuma， K． and Kobayashi， K．（1961）Mineralogical problems concerning Rapid clay mineral analysis of sedimentary rocks． Acta Univ． Carolinae， Geol． Suppl．，1：189－219．Tada， R． and Iijima， A．（1992）Lthostratigraphy and compositional variation of Neogene Hemipelagic sediments i 1 the Japan Sea． Proc． ODP， Sci． Res．，127／128：12291260． Tamaki， K， Pisciotto，KA， AllanJ． et．al．（1990）Proceedings of the ODP 127， 844p．
