DIAGENESIS OF DIOCTAHEDRAL AND TRIOCTAHEDRAL … 49/49-4-333.pdf · tion and development. Recently, detailed studies of I-S were made in the Tertiary sedimentary basin where fine-grained

Clays a~ut Clay Minerals, Vol. 49, No. 4, 333-346, 2001.

DIAGENESIS OF D I O C T A H E D R A L AND TRIOCTAHEDRAL SMECTITES FROM ALTERNATING BEDS IN MIOCENE TO PLEISTOCENE ROCKS OF

THE NIIGATA BASIN, JAPAN

BYEONG-KOOK SON 1, TAKAHISA YOSHIMURA 2"* AND HIKARU FUKASAWA 3

t Korea Institute of Geoscience and Mineral Resources (KIGAM), 30, Kajungdong, Yusungku, Taejon, Korea 2 Department of Environmental Sciences, Faculty of Sciences, Niigata University, Ikarashi-2, Niigata, Japan

3 Exploration Department, Japan Petroleum Exploration Co. Ltd, Higashi-Shinagawa, Tokyo, Japan

Abs t rac t - -Clay mineral diagenesis in the Niigata basin is documented by mineralogical and chemical analysis of clay minerals from cuttings from the Shinkumoide SK-1D (SSK-1D) well which is characterized by alternating beds containing dioctahedral and trioctahedral smectite minerals with increasing depth. Dioctahedral smectite shows a progressive increase in illite interstratification with increasing depth. The transition of dioctahedral smectite to interstratified illite-smectite (I-S) is supported chemically by an increase in K and A1 and a decrease in Si with increasing depth. In contrast, trioctahedral smectite (saponite) reacts to form a 1:1 interstratified chlorite-smectite (C-S) with increasing burial depth and temperature. Considering the geology and the occurrence of smectite, the SSK-1D smectites probably altered diagenetically from two different parent materials: dioctahedral smectite is derived from clastic sediments and transforms to interstratified illite-smectite, whereas trioctahedral smectite is derived from andesitic pyroclastic rocks and transforms to interstratified chlorite-smectite.

The C-S occurs at the same depth of --3200 m as the conversion of randomly interstratified (R = 0) I-S to (R = 1) I-S. Furthermore, the depth is compatible with a T~,~ temperature of 430-435~ which indicates the starting temperature for oil generation from organic matter. The temperature of the conversion of (R = 0) I-S to (R = 1) I-S and the start of corrensite formation is estimated at 110-120~ based on the time-temperature model suggested by others. The clay-mineral diagenesis in the SSK-1D further suggests that I-S and C-S can act as geothermometers in clastic and pyroclastic sediments provided that the effect of time is considered.

Key Words--Chlorite-Smectite, Clay Mineral Diagenesis, C-S, Geothermometer, Illite-Smectite, I-S, Niigata Basin, Saponite.

I N T R O D U C T I O N

The p rogress ive t r ans fo rmat ion of smect i te is volu- metr ica l ly the mos t impor t an t d iagenet ic clay reac t ion dur ing the progress ive bur ia l of s ed imen ta ry sequences; d ioc tahedra l smect i te t r ans forms into ill i te v ia in- t e r s t ra t i f i ed i l l i t e - s m ec t i t e ( I -S) , and t r i o c t a h e d r a l smect i te t r ans forms into chlor i te via interstrat i f ied ch lor i te - smect i te (C-S). T he t r ans fo rmat ion of diocta- hedra l smect i te to ill i te is wide ly recogn ized in fine- gra ined clast ic sed iments t h roughou t the wor ld (Perry and Hower, 1972; H o w e r e t a l . , 1976; Son and Yosh- imura, 1997). The reac t ion of d ioc tahedra l smect i te to illite is a con t inuous series of I-S; the propor t ion of illite layers in I-S increases wi th dep th in response to increas ing t empera tu re or t ime. The m e c h a n i s m of the smect i te- to- i l l i te reac t ion has been e x a m i n e d over the past few decades (Nadeau e t a l . , 1984; Al t ane r and Ylagan , 1997). In addi t ion, the s tudy of I-S d iagenes is has been s t imula ted part ly by an economic interes t in f inding more eff icient me thods to prospect for petroleum. Therefore , clay minera l d iagenes is has been ap- plied to pe t ro leum explora t ion as a g e o t h e r m o m e t e r to

* Present address: 7910-22, 2-No-Cho, Ikarashi, Niigata, Japan.

cons t ra in the the rmal h i s to ry of bas ins to predic t source- rock ma tu ra t ion be t te r (Es l inger and Pevear, 1988; Pyt te and Reynolds , 1989; El l iot t e t a L , 1991). The change of t r ioc tahedra l smect i te to ch lor i te is d o m i n a n t in sed iments associa ted wi th mafic vo lcan ic or evapor i t ic rocks (Yoshimura , 1983; C h a n g e t a l . ,

1986; Inoue and Utada, 1991; Hillier, 1993). In contrast to I-S wi th changes in layer propor t ions , the react ion invo lv ing t r ioc tahedra l smect i te has been con- s idered as a p rograde sequence of three phases: smectite, correns i te (1:1 C-S) and chlor i te (Shau e t a l . ,

1990; Inoue and Utada, 1991; Beaufor t e t a l . , 1997). Thus, corrensi te , the in te rmedia te par t of the sequence, is a discrete phase, ra ther than an inters t ra t i f icat ion o f smect i te and chlor i te layers. The n u m b e r of s tudies o f the t r ioc tahedra l smect i te - to-chlor i te t r ans fo rma t ion is l imi ted c o m p a r e d to those devoted to the t r ans forma- t ion of d ioc tahedra l smect i te to illite, p robab ly because C-S is res t r ic ted to mafic assoc ia t ions of vo lcanic las - tics or evapori tes .

In the Japanese is lands, I-S and C-S t r ans fo rmat ions have pr imar i ly been inves t iga ted as they relate to hy- d ro the rmal a l tera t ion ( Inoue and Utada, 1983; Inoue, 1987; Inoue e t a l . , 1987). However , several th ick sedimen ta ry sequences whe re the t rans i t ion o f smect i te to i l l i te or to chlor i te p robab ly occurs are p resen t in Ter-

Copyright �9 2001, The Clay Minerals Society 333

334 Son et al. Clays and Clay Minerals

Figure 1. Location of the Shinkumoide SK-1D well, and the distribution of marine sediments for each formation in the Niigata basin (modified from Sato et al., 1995). A deep section of turbidite facies is developed to the west of the dotted line. However, mudstone facies are dominant to the north and east of the line. Note that the Shinkumoide SK-1D well is located in the mudstone facies. LT Lower Teradomari Formation; UT--Upper Teradomari Formation; SY--Shiiya Formation; N Y - - Nishiyama Formation.

tiary sediments. In these sedimentary basins, many drill holes have been made for hydrocarbon exploration and development . Recently, detailed studies of I-S were made in the Tertiary sedimentary basin where fine-grained sediments dominate (Son and Yoshimura, 1997; Niu et al. , 2000). These studies indicated I-S diagenesis and showed a typical profile of smecti te similar to the Gul f Coast sediments (Hower et al . ,

1976). In this profile f rom Japan, we show that both dioctahedral and trioctahedral smectites occur in the same well.

The purpose of the present study is to document clay mineral diagenesis observed in the Shinkumoide SK-1D (SSK-1D) explorat ion well which samples > 4000 m of sediments ranging in age f rom Miocene to Pleistocene, in the Niigata sedimentary basin (Fig- ure 1). The well is dominated by fine-grained rocks including clastics and pyroclastics, and presents an ideal setting for clay mineral studies. This paper shows that the SSK-1D well displays both C-S and I-S re- actions with increasing burial depth. In addition, the clay mineral changes are correlated with organic maturity data to calibrate temperatures in the well.

G E O L O G I C A L S E T T I N G

The Niigata sedimentary basin is a very thick marine sequence of clastic and pyroclastic sediments

which accumulated during Miocene to Pleistocene. The basin was initially formed by the effect of rifting related to tensional back-arc spreading in Miocene t ime (Kobayashi and Yoshimura, 2000). In the Late Pl iocene to Pleistocene, Eas t -Wes t compress ion re- sulted in many Nor th -Sou th trending folds and faults in the basin. This movemen t produced uplift and erosion in the southwestern and northern parts o f the basin whereas, because of subsidence in the middle area of the basin, sedimentat ion continued after the Plio- cene. Subsequently, the northern region subsided and was filled with fine-grained sediments. Lithological ly, turbiditic sandstone predominates in the southern and western parts o f the Niigata basin, whereas mudstones prevail in the middle and northern regions (Figure 1).

The S S K - I D well is located in the middle of the basin, geographical ly west of Nagaoka City, Niigata Prefecture (Figure 1). The well is located within the region characterized mainly by mudstone sediments, and penetrates a sedimentary succession of 4820 m of Miocene to Pleiostocene strata in the Niigata sedimentary basin. The sequences are divided into six formations: Lower Teradomari, Upper Teradomari, Shiiya, Nishiyama, Ha izume and U o n u m a Formations, in as- cending order (Figure 2). The sequence o f these formations is little disturbed by tectonic movement , ex-

Vol. 49, No. 4, 2001 Diagenesis of dioctahedral and trioctahedral smectites 335

Figure 2. Diagrammatic cross-section of study area.

cept for gentle folds and faults in the Middle Pleisto- cene. The Lower and Upper Teradomari Formations consist primarily of clay-rich mudstones with occa- sional intercalation of tuff and sandstone. The deposition of the Teradomari Formation started at 14-13 Ma in a bathyal environment (Figure 3). During the Teradomari stage, a submarine fan developed in the southern part of the Niigata basin, while siliceous mudstone accumulated in the region including the SSK-1D well (Figure 1). The Shiiya Formation con- formably overlies the Teradomari Formation and is composed predominantly of andesitic pyroclastic rocks, also deposited in the bathyal environment at 7 Ma. During the Shiiya stage, the SSK-1D was also dominated by a deposit of gray fine-grained clastic and volcaniclastic mudstones which accumulated at a greater rate of sedimentation than other formations. The Nishiyama Formation, overlying the Shiiya For- mation, is composed mainly of fine mudstone with sandstone. The Nishiyama Formation includes dacite or andesite. Deposition of the Nishiyama Formation started at 4 Ma and in the SSK-1D is dominated by massive mudstone and sandy mudstone sequences. The Haizume and Uonuma Formations are also dominated by mudstones. Structurally, the formations at the SSK-1D well were folded gently and faulted by

East-West compression during the Middle Pleistocene (Kobayashi et al. , 1991). The SSK-1D as a whole is a bathyal sequence of fine mudstones, and thus an ideal well for the study of clay mineral diagenesis.

MATERIALS AND METHODS

Cuttings were sampled at intervals of 200 m throughout the well and were then hand-picked to en- sure representative lithology at different depths. Quan- titative analyses of whole-rock samples were obtained by powder X-ray diffraction (XRD) and using the computer program SIROQUANT (Sietronics, 1996). This program is designed for the quantitative analysis of mineral phases based on the Rietveld technique. Chemical analyses of the whole-rock samples were performed by X-ray fluorescence (XRF) spectrometry on fused glass beads.

Cuttings were ground gently in distilled water, and dispersed in an ultrasonic bath. The suspension was centrifuged to obtain the following size-fractions: >2 txm, <2 ~xm and <0.2 p~m. Following a filter trans- fer procedure (Moore and Reynolds, 1989), clay specimens of preferred orientation of the <2 ixm fractions were prepared for XRD. Oriented specimens of the <0.2 Ixm fractions were also prepared by pipetting the suspensions onto a glass slide. The <2 and <0.2 ~m specimens were air dried, saturated with ethylene glycol, and heated at 550~ before analysis. Profiles were generated using a Rigaku RINT 1200 diffractometer with Ni-filtered CuKc~ radiation at 40 kV and 20 mA. The ratio of illite and smectite in I-S was determined by comparing the patterns obtained to tracings calculated using NEWMOD (Reynolds, 1985). Detrital clay minerals interfere with the determination of the I-S ratio, thus the <0.2 Ixm fractions were used in the analysis to minimize contamination and interference from coarser clays, e.g. illite, chlorite and kaolinite. The octahedral character of each clay mineral was determined from the position of the 060 reflection on XRD (random mounts, <2 ixm fractions) and from chemical analysis.

Electron microprobe analyses were also performed on selected <0.2 Ixm clay powder samples that were prepared using the method of Son and Yoshimura (1997). Eight samples were selected for electron microprobe analysis: five of dioctahedral clays and three of the trioctahedral smectite (saponite), which include little or no clay mineral impurities except for kaolinite. To calculate the chemical formula of smectite and I-S, the amount of contaminating kaolinite, as determined by the quantitative analysis of the XRD patterns, was subtracted from the electron microprobe data.

Rock-Eval pyrolysis was performed on cuttings to obtain organic maturity data. About 100 mg of each sample was heated to 600~ in a Rock-Eval instrument (Espitali6 et al. , 1985).

336 Son et aL Clays and Clay Minerals

Figure 3. Stratigraphy, l i thology and burial history of the Shinkumoide SK-1D well.

Table 1. Mineral composi t ion of cuttings from the Shinku- moide SK-1D well.

wt. % of mineral

Depth Plagio- K-rich Amphi- Clays (m) Quartz clase feldspar Zeolite bole (+ micas)

1200 28.2 20.6 8.2 - - - - 43.0 1400 25.0 17.2 8.8 3.6 - - 45.4 1600 26.8 18.4 9.2 1.8 - - 43.8 1800 27.6 18.6 11.5 - - - - 41.3 2000 30.5 21.9 7.4 - - - - 40.2 2200 30.5 21.1 8.5 - - - - 39.9 2400 6.8 55.9 15.3 - - - - 22.0 2600 28.2 30.0 12.0 - - 4.7 25.1 2800 33.1 21,9 14.0 - - - - 31,0 3000 34.9 19.6 8.4 - - - - 37.1 3200 25,8 36.5 10.4 - - - - 27.3 3400 33.1 23.4 11.3 - - - - 32.2 3600 36.1 26.5 6.6 - - - - 30.8 3800 37.5 14.0 7.9 - - - - 40.6 4000 35.0 20.2 10.1 - - - - 34.7 4200 41.5 17.4 5.0 - - - - 36.1 4400 35.6 21.5 4.2 - - - - 38.7 4600 36.3 19.8 2.6 - - - - 41.3 4800 40.5 16.4 2.2 - - - - 40.9 4820 39.0 15.8 3.3 - - - - 41,9

R E S U L T S

Whole-rock mineralogy and chemistry

X - r a y d i f f r a c t i o n s h o w s t h a t the m u d s t o n e s p r i m a r -

i l y c o n s i s t o f c l a y m i n e r a l s a n d f i n e - g r a i n e d q u a r t z and

f e l d s p a r ( m a i n l y p l a g i o c l a s e ) (Tab le 1, F i g u r e 4). T h e

m u d s t o n e s a l s o i n c l u d e z e o l i t e ( c l i n o p t i l o l i t e ) a t sha l -

l o w d e p t h s and a m p h i b o l e a t a d e p t h o f 2 6 0 0 m. T h e r e

is a v a r i a t i o n in m i n e r a l a b u n d a n c e w i t h i n c r e a s i n g

d e p t h ; q u a r t z t e n d s to i n c r e a s e w i t h dep th , w h e r e a s

K - r i c h f e l d s p a r d e c r e a s e s . In c o m p a r i s o n , p l a g i o c l a s e

s h o w s a d i s t i n c t i n c r e a s e in a b u n d a n c e in i n t e r v a l s o f

a n d e s i t i c p y r o c l a s t i c r o c k s .

T h e c h e m i c a l c o m p o s i t i o n s o f s e l e c t e d m u d s t o n e s

a re s h o w n in T a b l e 2. T h e SiO2 c o n t e n t in m u d s t o n e

i n c r e a s e s w i t h dep th , p r o b a b l y r e l a t e d to the i n c r e a s e

in qua r t z . T h e M g O c o n t e n t is g r e a t e r in the i n t e r v a l s

b e t w e e n 2 0 0 0 - 4 0 0 0 m t h a n at d e e p e r a n d s h a l l o w e r

l e v e l s . T h i s v a r i a t i o n c a n be a t t r i b u t e d to a n d e s i t i c

p y r o c l a s t i c r o c k p r e s e n t at 2 0 0 0 - 4 0 0 0 m.

Mineralogy of interstratified illite-smectite

C l a y s a m p l e s a re c h a r a c t e r i z e d b y h i g h i l l i t e and

k a o l i n i t e c o n t e n t s , t h e r e b y m a k i n g the q u a n t i t a t i v e es-

t i m a t i o n o f i n t e r s t r a t i f i e d c l a y - m i n e r a l c o m p o s i t i o n

d i f f icu l t . T h e < 2 p.m c l a y f r a c t i o n s are s i g n i f i c a n t l y

c o n t a m i n a t e d by de t r i t a l m i n e r a l s s u c h as q u a r t z a n d


Figure 4. Change in whole-rock mineralogy with depth.

d iscrete illite. In compar i son , the < 0 . 2 Ixm frac t ions are near ly monomine ra l i c , thus a l lowing an accurate a s sessment o f I-S.

Cut t ings f rom dep ths o f 1 2 0 0 - 2 0 0 0 m conta in mos t ly d ioc tahedra l phases , wh ich are conf i rmed by the 060 ref lect ion at 1.499 A (Figure 5). Dioc tahedra l smect i te in air-dried spec imens has a 001 ref lect ion at

12 ]~. Af ter t r ea tment wi th e thy lene glycol, the pattern displays an in tegral series of h igher -order reflec- t ions in addi t ion to the f irs t-order ref lect ion at 16.7 ]~. Ca lcu la ted pa t te rns indica te that the smect i te has an illi te layer con ten t o f < 2 0 % .

R a n d o m l y interstrat i f ied (R = 0) I-S wi th - -45% illite layers also occurs at depths of 2800 and 3000 m. The X R D profile shows that c o n t a m i n a n t clay minera l s such as kaol in i te and discre te ill i te are present despi te the use o f the < 0 . 2 txm fract ion.

R a n d o m l y interstrat i f ied I-S is not present in samples be low 3400 m; only ordered (R = 1) I-S is p resen t be low this depth. Illi te layers in the (R = 1) I-S increase wi th increas ing buria l depth. A representa t ive pa t tern of the (R = 1) I-S wi th 80% i l l i te- layer conten t shows an in tense ref lect ion at 11.1 ,~, wh ich is a com- b ina t ion peak of the I-S 002 ref lect ion (24 Pal2 = 12 ,~) and the ill i te 001 ref lect ion (10 ,~). Af ter satu- ra t ion wi th e thy lene glycol, two peaks are reso lved at 12.5 and 9.8 A (Figure 5). The 12.5 A reflect ion is a

Table 2. Chemical analyses of cuttings from the Shinku- moide SK-1D well.

1600 rn 1800 m 2200 m 3200 m 3000 m

Sit2 61.22 63.18 61.53 62.09 61.79 A1203 15.96 15.66 15.71 15.54 15.41 Fe2031 5.87 4.91 6.27 5.24 6.72 C a t 1.68 1.49 1.41 3.27 2.22 MgO 2.00 1.95 2.69 2.53 3.11 K20 3.13 3.24 2.84 2.74 2.83 Na20 2.37 2.51 2.43 3.02 2.32 Ti t2 0.70 0.64 0.68 0.52 0.65 MnO 0.05 0.05 0.06 0.08 0.08 PzO5 0.15 0.11 0.11 0.13 0.12 LOF 6.75 6.00 6.05 4.47 4.47 Total 99.88 99.74 99.78 99.63 99.72

3 6 0 0 m 4 0 0 0 m 4 2 0 0 m 4 6 0 0 m 4 8 2 0 m

S i t 2 63.00 64.34 65.25 64.16 64.29 A1203 15.25 15.35 14.73 15.64 15.81 Fe2031 6.99 6.05 5.84 6.19 6.07 C a t 1.23 1.20 1.34 0.80 0.85 MgO 2.64 2.20 1.99 1.96 2.02 K20 3.02 3.13 2.80 2.97 2.94 Na20 2.08 2.01 2.07 2.23 2.16 T i t 2 0.66 0.64 0.62 0.64 0.61 MnO 0.05 0.05 0.06 0.06 0.05 PzOs 0.09 0.08 0.08 0.08 0.08 LOF 4.79 4.74 4.96 5.08 4.94 Total 99.80 99.79 99.74 99.81 99.82

1 Total Fe as FezO 3. z LOI: loss on ignition.

co mb i n a t i o n of the I-S 002 peak (27 A /2 = 13.5 A) and illi te 001 peak (10 ,~), and the 9.8 ~, peak is f rom the illite 001 and the I-S 003 peaks (27 A/3 = 9 ,~). The sample pa t te rn ma tches a s imula ted pa t te rn wi th 80% illite layers and 2 0 % smect i te layers. Laye r propor t ion and order ing type for inters t rat i f ied I-S are pre- sented in Table 3.

Mineralogy of interstratified chlorite-smectite

Trioctahedra l smect i te (saponi te) is p resen t in samples at depths of 2 2 0 0 - 2 6 0 0 m. T h e saponi te has a f i rs t-order basa l ref lect ion at - -14.4 ,~ (Figure 6). U p o n sa tura t ion wi th e thy lene glycol, a sharp 001 ref lect ion is p resent at 17.2 A. A n integral series of h igher -o rder ref lect ions is also present in the g lycol - t rea ted samples and correla tes wel l w i th ca lcula ted pa t te rns for saponite. The 060 ref lect ion is at 1.537 A, ind ica t ing tr ioc- tahedra l character.

Correns i te , regular ly ordered (1:1) ch lor i te - smect i te (C-S), is p resent at 3200 m of the S S K - 1 D well. T h e correns i te is charac te r ized by a s t rong snper la t t ice re- f lect ion at - 2 9 . 2 ,~ in the air-dried state and the peak shifts to 31.1 ,~ after g lycola t ion (Figure 6). O the r re- f lect ions shift f rom 15.6 to 14.1 ,~ and f rom 7.8 to 7.1 .A wi th e thy lene glycol. The super la t t ice ref lect ion of correns i te is weak in X R D pat te rns of the < 0 . 2 Ixm fract ion. In the < 2 Ixm fract ion, however , the super- lat t ice ref lect ion is s t rong and sharp and illite, kaol in i te


16.7 A

1.499 A

57 61 65 (0 6 O)

1600 m (< 2 l~m, random)

. u

O~ l "

(1) i -

n

1600 m (13%I)

. . . . . . " * " 3000 m (42%I)

12.5A98 k

\ ' ' ~ r ~ 4 8 2 0 m (80%i)

i 1 1 1 i l l i l l l i l i l l I T i i l J l I I i i l l i i l l

5 10 15 20 25 30 35

~ Figure 5. Powder X-ray diffraction patterns of dioctahedral phases. The 060 reflection at 1.499 A. indicates dioctahedral character. I--illite; K--kaolinite; I-S--interstratifled illite-smectite.

and quartz are also present in significant amounts. Heat ing at 550~ produces a peak at - -12 A. The trioctahedral character of corrensite is shown by the 060 peak posit ion at 1.543 A.

Chemistry o f interstratified illite-smectite

The I-S in seven samples of each <0 .2 I~m size- fraction sample was analyzed by electron microprobe, and averages are g iven in Table 4 in order o f increasing percentage o f illite layers. Samples were analyzed from the shallowest and deepest depths in the well; in the middle depth interval there are no pure samples, even for the <0 .2 t~m fractions. The chemical analyses of three samples, f rom 4200, 4400 and 4800 m, were corrected for kaolinite impurities. In addition, the to-

tals were normalized to 100% for comparison (Ta- ble 4).

The K and A1 contents increase with increasing burial depth, whereas silica content decreases (Fig- ure 7). Illite layers in I-S also increase proportionally with increasing depth of burial. The chemical data are consistent with smectite diagenesis where A1 is sub- stituted for Si and interlayer K increases. On average, M g O content increases with depth in shal low intervals, but shows a relat ive decrease in the deepest samples at - 4 8 0 0 m. The increase in M g O content at

1800 m probably reflects the andesitic composi t ion of the rocks present.

Layer charge was plotted (Figure 8) in the triangular diagram of Srodofi and Eberl (1984). The data for I-S


Table 3. Layer proportions of the interstratified clay minerals from the Shinkumoide SK-1D well.

% I in I-S Depth (m) (<0.2 txm) Reichweite (R) % C in C-S Reichweite (R)

1200 14 R = 0 1400 20 R = 0 1600 13 R = 0 1800 10 R = 0 2000 20 R = 0 2200 2400 2600 2800 46 3000 42 3200 3400 65 R = 1 3600 70 R = 1 3800 70 R = 1 4000 75 R = 1 4200 75 R = 1 4400 80 R = 1 4600 80 R = 1 48OO 80 R = 1 4820 80 R = 1

0 R = 0 0 R = 0 0 R = 0

50 R = 1

is also charac te r ized by h igh WA1 and VXFe, and is s l ightly r icher in A1 than saponi tes repor ted f rom else- where in Japan (Figure 9). The Al - r i ch charac te r suggests tha t the saponi te f rom the S S K - 1 D wel l is de- r ived f rom fine andesi t ic vo lcan ic material .

Ana lyses of the S S K - 1 D saponi te show a low total oc tahedra l occupancy of 5 .3 -5 .5 pe r 22 oxygens (Ta- ble 5), wh ich is wel l be low the ideal va lue of 6.0. This oc tahedra l vacancy is p robab ly a t t r ibutable to the ox- idat ion of an or ig inal ly fe r roan saponite. I ron- r ich saponi te is, in general , uns tab le unde r a tmospher i c con- di t ions when r e m o v e d f rom its e n v i r o n m e n t (Badaut et aL, 1985). The r ep l acemen t of O H by O in the octa- hedra l coord ina t ion o f Fe 3+ is r espons ib le for the low total oc tahedra l occupancies . Indeed, the or ig inal Fe 2+ conten t of the S S K - 1 D saponi te can be ca lcula ted by mul t ip ly ing the present Fe 3§ con ten t by 1.5. This would lead to an increase f rom Fel.25 to Fe~.88 in the fo rmula in Table 5, and thus increases the total octa- hedra l occupancy to 6.0.

D I S C U S S I O N

at 1200 and 1800 m plot wi th in the range of smect i te and r a n d o m I-S, whi le those f rom 4200, 4400 and 4800 m plot wi th in the field of ordered I-S. Thus, the layer-charge data are in good ag reemen t wi th I-S rat ios and order ing types de te rmined by XRD. In this triangular d iagram, moreover , the layer-charge data show a notab le t rend increas ing toward h igher te t rahedra l sheet charge.

Chemistry of trioctahedral smectite

The chemica l data for correns i te f rom 3200 m were not ava i lab le because c o n t a m i n a n t minera l s are present in s ignif icant amount s in the < 0 . 2 Ixm fraction. How- ever, samples f rom 2200 to 2600 m are c o m p o s e d of near ly pure smecti te , wh ich was ana lyzed in detail . E lec t ron -mic roprobe analyses indica te that the clay f ract ions f rom 2200, 2400 and 2600 m consis t of smect i te (saponi te) of t r ioc tahedra l na ture (Table 5). In general , saponi te is charac te r ized by a h igh M g content in the oc tahedra l sites. However , saponi te f rom the S S K - 1 D has a h igh con ten t of oc tahedra l A1 and Fe. In Japan, saponite , C-S and chlor i te are c o m m o n in pyroclas t ic rocks o f the Green Tuff Fo rma t ions of M i o c e n e age. Saponi te occurs in two modes: cavi ty fill ings prec ip i ta ted f rom solut ion and r ep l acemen t of vo lcan ic glass. Saponi te infi l l ing cavi t ies c o m m o n l y has a h igh Fe con ten t and low A1 content , whereas saponi te rep lac ing vo lcan ic glass has h igh A1 and Fe conten ts (Yoshimura , 1983). Acco rd ing to that author, t r ioc tahedra l clay minera l s f rom the Green Tuff For- mar ion have a greater A1 con ten t than those f rom deep- sea basalts . The S S K - 1 D saponi te occurs at midd le dep ths in the wel l ( 2 2 0 0 - 2 7 0 0 m) where andesi t ic pyroclas t ic rocks are abundant . The S S K - 1 D saponi te

Alternation of dioctahedral and trioctahedral smectites

In the S S K - 1 D sequence, we note that d ioc tahedra l and t r ioc tahedra l clay minera l phases occur a l ternate ly th roughou t the wel l (Figure 10). The wel l p rov ides a rare oppor tuni ty to show dioc tahedra l and t r ioc tahedra l c lay-minera l d iagenesis . In the reg ion inc lud ing the well , s ed imen ta t ion and subs idence were re la t ively un i fo rm th roughou t thei r dura t ion wi thou t s ignif icant deformat ion , a l though there are gent le folds and faul ts caused by compres s ion in the Midd le Ple is tocene: the sed imen ta ry sequences are depos i ted c o n f o r m a b l y in a mar ine e n v i r o n m e n t dur ing Midd le M i o c e n e to Pleis- tocene time. In addit ion, there are no hyd ro the rma l ly in t rus ive bodies .

The l i thology is charac te r ized by the occur rence of f ine-gra ined clastic rocks in te rbedded wi th pyroclas t ic rocks present wi th in the sampled interval . Dioc tahedral smect i te and t r ioc tahedra l smect i te (saponi te) are present in the upper in terval : the d ioc tahedra l smect i te at depths of 1 0 0 0 - 2 0 0 0 m domina t ed by clastics, and the t r ioc tahedra l smect i te at depths o f 2 2 0 0 - 2 6 0 0 m charac te r ized by pyroclast ics . Cons ide r ing the depo- si t ional h i s to ry of the su r rounding sed iments and the occur rence of the smecti te , the S S K - 1 D smect i tes have p robab ly al tered d iagenet ica l ly f rom two paren t volcanic mater ia ls : d ioc tahedra l smect i te at depths o f < 2 0 0 0 m is der ived f rom acidic volcanic mater ia l s and t r ioc tahedra l smect i te at 2 2 0 0 - 2 6 0 0 m is de r ived f rom basic Mg,Fe- r i ch volcanic mater ials . As the dep th of buria l increases , the d ioc tahedra l smect i te reacts to fo rm I-S at 2 8 0 0 - 3 0 0 0 and 3 4 0 0 - 4 8 2 0 m, whereas the t r ioc tahedra l smect i te conver t s into a 1:1 regular ly interstrat i f ied C-S at a dep th of 3200 m. T h r o u g h o u t


1.537 k

Figure 6. characten

. m

g ) r

2400 m D p I p I ~ I j I ( < 2 1 a m ' random)

57 61 65

(060)

saponite

corrensite

~" ~ 2400 m

~ ~ 3200 m

5 10 15 20 25 30 35

~ Powder X-ray diffraction patterns of trioctahedral phases. The 060 reflection at 1.537 A reveals the trioctahedral

the interval, as a consequence, I-S and C-S transitions occur alternately: S --~ I-S ~ I and S --* C-S --~ C.

Diagenesis of dioctahedral smectite

The I-S transformation is recognized in sedimentary basins worldwide. In the SSK-1D well, the alteration of dioctahedral smecti te to I-S conforms to the illitization reaction with an increasing amount of illite layers in response to increasing burial depth. The I-S diagenesis is similar to that of the Gul f Coast (Hower et al., 1976), although trioctahedral smecti te and C-S are also present. In the SSK-1D well, the clay mineralogical changes are probably the result o f temperature increase associated with burial, because no evidence o f igneous or hydrothermal activity was found in the study area.

For the I-S reaction, the pattern of increasing the proportion of illite layers varies among different sedimentary basins wor ldwide (Srodofi and Eberl, 1984). Differences depend primarily on the availability of K,

temperature and time. The negat ive layer charge of the clay becomes sufficiently large to fix K in the inter- layers. In the SSK-1D well, the layer charge of I-S increases in the tetrahedral sheet with increasing depth (Figure 8). Moreover, the K and A1 contents tend to increase with depth, whereas the Si content decreases (Figure 7), such that: smecti te + A13++ K-- --~ illite + Si 4+. In the SSK-1D well, the abundance of K-rich feldspar decreases with depth (Figure 4), thus indicat- ing that K-rich feldspar is the most l ikely source of K for the I-S reaction. The potassic feldspar is, however, present in trace amounts throughout the well. In addition to the potassic feldspar, therefore, discrete illite, which occurs throughout the well, can be considered as another source of K for the illitization. Futhermore, some I-S may provide the components required to make a more illitic I-S (Pollastro, 1985).

The most striking factor in the I-S reaction is its dependence on temperature. T ime is also an important factor in the diagenetic reaction of I-S. In the Gul f


Table 4. Electron microprobe analysis of interstratified illite- smectite (I-S) from the Shinkumoide SK-ID well.

S a m p l e dep th (% ! in I -S)

1200 m 1800 m 4 2 0 0 rn I 4 4 0 0 m t 4 8 0 0 na t ( 1 4 % I) ( 1 0 % I) ( 7 5 % I) ( 8 0 % I) ( 8 0 % I)

SiO2 62.97 64.10 56.46 56.80 56.33 A1203 22.73 21.92 26.73 25.84 25.81 FezO~ 2 7.36 6.83 6.42 6.24 6.91 MgO 2.81 3.42 3.51 3.46 3.30 MnO 0.03 0.06 0.05 0.04 0.02 CaO 0.98 1.07 0.37 0.40 0.57 Na20 0.89 1.47 1.05 1.05 0.72 K20 2.23 1.12 5.41 6.17 6.34 TotaP 100.00 100.00 100.00 100.00 100.00

Numbers of cations on the basis of O20(OH)4

Si 7.61 7.70 7.00 7.06 7.03 At (IV) 0.39 0.30 1.00 0.94 0.97 ]s tet. 8.00 8.00 8.00 8.00 8.00 AI (VI) 2.85 2.81 2.90 2.85 2.82 Fe 0.67 0.62 0.60 0.58 0.65 Mg 0.51 0.61 0.65 0.64 0.61 Mn 0.00 0.01 0.00 0.00 0.00

oct. 4.03 4.04 4.15 4.08 4.08 Ca 0.13 0.14 0.05 0.05 0.08 Na 0.21 0.34 0.25 0.25 0.17 K 0.34 0.17 0.86 0.98 1.01

int. 0.68 0.65 1.16 1.29 1.26 Tet. chg 0.39 0.30 1.00 0.94 0.97 Oct. chg 0.42 0.49 0.20 0.40 0.36 Int. chg 0.81 0.79 1.21 1.34 1.34

Analysis corrected for kaolinite 2 Total Fe as Fe203. 3 Total normalized to 100%.

impurity.

Coas t region, for instance, the younge r rocks have ob- viously not changed as m u c h as the old ones, wh ich suggests that the smect i te- to- i l l i te reac t ion is kinet i - cal ly con t ro l led as a func t ion of t ime. Based on tempera ture and geologica l age, Pol las t ro (1993) p roposed t ime- tempera tu re mode ls for I-S geo the rmal studies. The conve r s ion o f ( R = 0) I-S to (R = 1) I-S is as- s igned to 100-110~ for s ed imen ta ry rocks of Mio- cene age or o lder ( 5 - 3 0 0 Ma) (Hof fman and H o w e r model ; Pollastro, 1993). For younge r rocks ( < 3 Ma), however , the I-S conve r s ion is at a h igher t empera ture of 120-140~ (short- l i fe geo the rma l mode l ; Pollastro, 1993). In the S S K - 1 D well , (R = 0) I-S t r ans forms at - 3 2 0 0 m where correns i te occurs; (R = 1) I-S is found at < 3 2 0 0 m. Therefore , the conve r s ion of (R = 0) I-S to (R = 1) I-S is es t imated to occur at a dep th of 3200 m. I f the t t o f f m a n and H o w e r model is ap- plied to the convers ion , the dep th o f 3200 m is as- s igned to 100M 10~ However , i f the short- l i fe mode l is appl ied, the same depth can be ass igned to 1 2 0 - 140~

Diagenesis o f trioctahedral smectite

In cont ras t to d ioc tahedra l smecti te , t r ioc tahedra l smect i te (saponi te) is conver t ed direct ly to C-S in the

S S K - 1 D well wi thou t any con t inuous increase in chlo- ri te layers. Some inves t iga tors (e.g. C h a n g et al., 1986) in te rpre ted the C-S reac t ion as a series of inters t rat i f ied ch lor i te -smect i te phases , ana logous to the smect i te- to- ill i te react ion. However , in mafic assoc ia t ions wi th volcanic las t ic sediments , correns i te is cons ide red a d iscre te mineral , ra ther than an inters t ra t i f icat ion of smect i te and chlor i te layers (Shau et aL, 1990; Inoue and Utada, 1991; Beaufor t et al., 1997). Acco rd ing to m a n y studies, the S --~ C-S --~ C t rans i t ion does not invo lve a con t inuous increase in the n u m b e r o f ch lor i te layers. Instead, a discrete rat io of smect i te and chlor i te layers occurs wi th a discrete stabil i ty field. Recent ly , C-S wi th > 5 0 % chlor i te layers was re in terpre ted as a physical mix tu re o f correns i te (1:1 C-S) and chlor i te (i.e. chlor i te + corrensi te) , r a ther than as inters t ra t i f ied ch lor i te -smect i te (Hillier, 1993).

The S S K - 1 D saponi te is conver t ed to correns i te at a dep th of 3200 m. The fo rmat ion o f correns i te f rom smect i te requires the fo rmat ion o f a bruc i te - l ike com- ponent , and that reac t ion can be wr i t ten as: Mg2++ 2HzO ---) Mg(OH)2 + 2H § In the S S K - 1 D well , saponi te is a poss ib le precursor of C-S. Saponi te and corrensi te occur in the same l i thology where andesi t ic vo lcanic las t ic rocks are p redominan t . The S S K - 1 D saponi te is an uns tab le phase, p robab ly because o f its h igh Fe and A1 content . Bu lk - rock analys is shows that M g is present in abundance (Table 2) at depths of 2 0 0 0 - 2 4 0 0 m, where saponi te exists. Thus , saponi te can p robab ly readi ly t r ans fo rm to more s table corrensite. Consequent ly , the S S K - 1 D correns i te is conve r t ed d iagenet ica l ly f rom saponi te by the fo rmat ion of M g ( O H ) 2 sheets.

Temperature o f smectite diagenesis

Trans fo rmat ion of the clay minera l phases was com- pared wi th Tma x values ob ta ined f rom organic mat te r in muds tones by Rock -Eva l pyrolysis (Table 6; Fig- ure 10); Tin, X is a pyrolysis t empera tu re where the rate of genera t ion o f hyd roca rbon is at a m a x i m u m dur ing the Rock-Eva l pyro lys is reac t ion (Espital i6 et aL, 1985). The T~ax va lue is a r easonab le measure o f the the rmal matur i ty of organic matter. Bu r tne r and Warn- er (1986) found a good corre la t ion be tween the per- cen tage of smect i te layers in I-S and Tm,x. The Tma ~ va lue of 4 3 0 - 4 3 5 ~ the start ing t empera tu re for oil genera t ion, ma tches wel l wi th the conve r s ion o f (R = 0) I-S to (R = 1) I-S. In the S S K - 1 D well, correns i te first occurs at a dep th of 3200 m. Moreover , the order ing type o f I-S changes at the same dep th where correns i te appears, f rom R = 0 above 3200 m to R = 1 order ing be low this depth. The Rock -Eva l pyrolys is of organic mat te r in the S S K - 1 D m u d s t o n e s shows a gradual increase in Tmax value, as s h o w n in Table 6 and Figure 10. Fur the rmore , a Tm,x t empera tu re o f near ly 4 3 0 - 4 3 5 ~ wh ich is the start of oil genera t ion , occurs to a depth of - -3200 m (Figure 10). The indi-


1000

2000

E c-

~ '3000

4000

5000

% SiO2 54 56 58 60 62 64

, ~ . i �9 , I I I | i I

/

/

/

/

/

% /

, " = , , - , - ',

/

/ I � 9

/

/

I

/

66 20 1000

2000

E v

(.-

~. 3000'

4000

5000

% AI203 24

i I

t O �9 �9 %

O ~

\

\

i |

28 I

\

\ i

\

Figure 7.

0 1 0 0 0

E v

e"

~- 3000, O

% K20 2 4 6 8

t I i a I . I

~ m Q

Q \

2000' \

k

k

4 0 0 0

5000 ~ , ,

%

\

\

\

tD O

I w I i

Compositional variation in interstratified I-S with depth.

% MgO 2 3

1 0 0 0 ' '

, l ~ O

2000'

E v

~ 3 0 0 0 ,

4000'

5000

I

m

w

I

cators for the degree of diagenesis are consistent: the depth at which (R - 0) I-S is converted to (R = 1) I- S coincides with the depth where corrensite appears and Tma ~ of 430-435~ Thus, the depth of 3200 m is assigned to 100-110~ in accord with the Hoffman and Hower model (Pollastro, 1993). Inoue and Utada (1991) reported that corrensite formed at temperatures of 100-200~ in thermally altered volcaniclastic rocks. This result is consistent with the data here. In addition, Hillier (1993) showed that corrensite occurs at 1 2 0 - 2 6 0 ~ in Devonian lacustrine mudrocks. Iijima and Utada (1971) reported that the formation of corrensite at the expense of trioctahedral smectite was observed at a depth equivalent to 85-95~ which was assigned to the analcime zone. This temperature of

first appearance of corrensite was used as a paleoth- ermometer in subsequent studies (Hoffman and How- er, 1979; Pollastro, 1993). Niu et al. (2000) studied I- S diagenesis in six wells in the Niigata basin. They showed that there are significant differences between wells at the depth of transition to (R = 1) I-S. The difference may relate either to the influence of other parameters besides temperature, or to uncertainty in the temperatures measured in drill holes, which is ne- glected in this study. In the Niigata basin, however, a more important factor affecting the difference in the transi{ion of I-S ordering may be tectonic deformation during the Pliocene or Pleistocene. Differences between wells in the depths of transition to the ordering of (R = 1) I-S may be caused by differences in uplift


Muscovite

~ ~ �9 1200 m

-F 1 8 0 0 m

. . . . . ~" [] 4200 m

�9 -"~ / " \ ~' �9 4400 m ~ Illite i

, . , , ~ X 4 8 0 0 m

10%

�9 ~ .:o Ordered I-S

45%�9 o . , , o � 9

Random I-S �9 " ~ ' �9 Smectite Celadonite �9 Leucocite ' ' ' ' ' ' ' '

, Increasing Octahedral Charge Pyrophyllite

Figure 8. Interstratified I-S plotted within the triangular composition diagram muscovite-celadonite-pyrophyllite (the curves of percent smectite layers are from Srodofi and Eberl, 1984). Arrow indicates a trend of increasing tetrahedral layer charge.

and erosion, b ecause burial and tectonic his tor ies va ry

cons ide rab ly b e tween areas where the wel ls are locat-

ed.

Acco rd in g to t empera tu re data obta ined f rom the Ja-

pan Pe t ro l eum Explora t ion C o m p a n y , the geo the rma l

gradient at the S S K - I D well is 3 .10~ m (Figure

11), and the p resen t t empera tu re at 3200 m is 115~

s l ight ly h ighe r than the t empera tu re o f 1 0 0 - 1 1 0 ~ as-

s igned to this depth by the H o f f m a n and H o w e r mode l

(Pollastro, 1993). However , the S S K - 1 D well conta ins

rocks y o u n g e r than M i o c e n e age in the uppe r two

thirds o f the profile. Fur the rmore , the I-S c onve r s ion

Table 5. Electron microprobe analysis of saponites from the Shinkumoide SK-1D and their comparison with other saponites.

Indue and Niu and Sudo Utada Yoshimura Kimbara

2 2 0 0 m 2 4 0 0 m 2 6 0 0 m (1954) (1991) (1996) (1975)

SiO2 50.64 51.69 48.57 39.68 44.18 55.97 40.53 A120 3 12.35 12.49 13.07 3.93 7.86 9.26 12.20 Fed I 10.46 10.65 13.77 18.95 15.34 16.20 12.11 MgO 13.35 13.31 12.56 11.21 15.64 14.21 14.44 MnO 0.12 0.11 0.20 0.19 0.08 0.00 0.20 Cad 0.79 0.82 0.47 2.37 2.68 3.65 3.24 Na20 1.94 1.23 1.23 0.00 0.00 0.21 0.48 K20 0.79 0.81 2.31 0.00 0.30 0.50 1.04 Total 90.44 91.11 92.18 76.33 86.08 100.00 84.24

Numbers of cations on the basis of O20(OH)4

Si 7.18 7.25 6.95 7.18 6.87 7.35 6.41 A1 (IV) 0.82 0.75 1.05 0.82 1.13 0.65 1.59

tet. 8.00 8.00 8.00 8.00 8.00 8.00 8.00

AI (VI) 1.25 1.31 1.15 0.02 0.31 0.79 0.69 Fe 1.24 1.25 1.65 2.87 1.99 1.78 1.60 Mg 2.82 2.78 2.68 3.02 3.62 2.78 3.41 Mn 0.02 0.01 0.03 0.03 0.01 0.00 0.03

oct. 5.33 5.35 5.51 5.94 5.94 5.35 5.73

Ca 0.12 0.12 0.07 0.46 0.45 0.51 0.55 Na 0.53 0.34 0.34 0.00 0.00 0.05 0.15 K 0.14 0.15 0.42 0.00 0.06 0.08 0.21

int. 0.79 0.61 0.83 0.46 0.51 0.64 0.91

All Fe calculated as Fed.

344 Son et al. Clays and Clay Minerals"

AI AI

< / " 2400 m " ~ / 2200 m Oo ,,2600 rn " ~

/" Kimbara oNiu and Yoshimura "NkA

/ " ,noue and Utada " ~ /~ o Sudo

Mg, , , , , , , , , Fe

Figure 9. Position of saponite analyses within the triangular composition diagram of A1-Mg-Fe. Data include analyses of saponites from the Shinkumoide SK- 1D (solid circle) and other saponites (open circle) from Kimbara (1975), Inoue and Utada (1991), Sudo (1954) and Niu and Yoshimura (1996).

also occurs in the Shi iya Format ion , mos t ly depos i ted dur ing the P l iocene (Figure 2). Therefore , the short- life model can also be appl ied to the well for es t imat- ing pa leo tempera tures . Accord ing to this model , the dep th of 3200 m can be ass igned to 120-140~ As- suming that the pa leo -geo the rma l grad ien t was near ly the same as the present geo the rma l gradient (Fig- ure 11), the H o f f m a n and H o w e r t empera tu re is lower by --10~ than the present tempera ture , p robab ly in- d ica t ing a subs idence of -- 320 m in depth based on the geo the rmal gradient . I f the short- l i fe mode l is appl icable, the pa loeo tempera tu re is grea ter by --15~ than the present temperature , thus ind ica t ing an uplif t of - -500 m. The region incorpora t ing the s tudy well was regional ly de fo rmed by an E a s t - W e s t compres - s ion dur ing the Midd le Ple is tocene (--0 .7 Ma) (Ko- bayash i et al. , 1991). Cons ide r ing the effect of the compress ion , the d i f ference be tween present and pa- l eo tempera tures at a g iven dep th may be caused by upl i f t or subs idence dur ing the Ple is tocene. Uplif t , ra ther than subs idence , is more likely, based on the c ross - sec t ion (Figure 2). However , a re la t ive subsi-

Table 6. Total organic carbon content (TOC) and Tin, X value by Rock-Eval pyrolysis of the mudstones from the Shinku- moide SK-1D well.

Depth (m) TOC (%) T.,~ (~

1200 0.51 422 1400 0.66 417 1600 0.73 424 1800 0.66 420 2000 0.67 418 2200 0.69 428 2400 0.0! 408 2600 0.17 423 2800 0.64 422 3000 0.60 433 3200 0.25 428 3400 0.50 434 3600 0.51 434 3800 0.36 435 4000 0.26 442 4200 0.48 438 4400 0.35 444 4600 0.47 444 4800 0.38 440 4820 0.50 447

dence can also occur on the under ly ing side o f a re- verse fault, wh ich would be reflected in a pa leotem- pera ture lower than the present t empera tu re at greater depths (Son and Yoshimura , 1997). In the S S K - 1 D well, the in te rva l of the occur rence of correns i te is cons is ten t wi th tha t of conve r s ion of (R = 0) I-S to (R = 1) I-S. Therefore , the t empera ture of fo rmat ion of corrensi te is s imilar to the t empera ture of I-S convers ion. The profi le of S S K - 1 D includes the geologica l t ime of 3 -5 Ma, which is not covered by e i ther the H o f f m a n and H o w e r mode l ( 5 - 3 0 0 Ma) nor the short- life model ( < 3 Ma). Consequent ly , the t empera tu re at wh ich correns i te fo rmat ion c o m m e n c e d in the SSK- 1D well is es t imated to be 110-120~ taken f rom the

Figure 10. Comparison of variation in clay mineral with Tma x data by Rock-Eval pyrolysis. Note an alternate occurrence of dioctahedral and trioctahedral phases and an increase in illite layers of I-S.


Figure 11. Present-day temperatures and paleo-temperatures deduced from two I-S geothermometry models.

upper temperature o f the Hof fman and Hower model and lower value of the short-l ife model .

A C K N O W L E D G M E N T S

The authors are grateful to the Japan Petroleum Exploration Company (JAPEX) for supplying cuttings and granting per- mission to publish the results. The first author thanks the Ja- pan Society for the Promotion of Science (JSPS) for provid- ing financial support for his study at Niigata University. The manuscript was significantly improved by the comments of S. Guggenheim, D. McCarty, R Ryan and an unidentified re- viewer. This research was supported in part by the NRL program from Korea Ministry of Science and Technology.

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E-mail of corresponding author: [email protected] (Received 11 May 2000; revised 22 February 2001; Ms'.

448; A.E. Douglas K. McCarty)

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DIAGENESIS OF DIOCTAHEDRAL AND TRIOCTAHEDRAL … 49/49-4-333.pdf · tion and development. Recently, detailed studies of I-S were made in the Tertiary sedimentary basin where fine-grained