hoiocene stratigraphy and paleoenvironments in …...the authors have investigated the stratigraphy...

HoIOCene Stratigraphy and Paleoenvironments in the Kanto

Plain, in relation to the Jomon Transgression*

Kunihiko ENno**. Katsuhisa SEKIMOTO**

and Tsukasa TAKANO**

(Received November 7, 1981)

1 Introduct,ion

The Kanto Plain, the biggest sedimentary basin in Japanese Islands, is situated in

the middle Honshu Island, having very thick and almost continuous deposits ranging

from Pliocene to Holocene time. Geomorphologically, several marine and fluvial terraces

formed during the last interglacial and the last glacial ages, occupy the most extensive

area in the Plain. Moreover, deep valleys dissecting these topographies are buried with

deposits of the latest Pleistocene to the Holocene to become flat and broad alluvial

lowl ands.

Two transgressions, in the latest Pleistoce-ne and in the early to middle Holocene,

played great roles in rapid accumulation and forming extensive alluvial surfaces. Especially

in the early Holocene, a great number of dissected valleys, including the main valleys

such as the Paleo-Ara river, the Paleo-Kinu river, and these tributaries, and small

valleys in the Kanto Plain, got drowned by the sea water invasion, which is called the

Jomon Transgression (Holocene Transgression) in Japan. This transgression in the Kanto

Plain was proposed first on the basis of archaeological evidences of marine shell-midden

and its distribution (ESAKA, 1972 ; et al.).

The authors have investigated the stratigraphy of the deposits filling the drowned

valleys, especially in the southern Kanto Plain characterized by rernarkable seismic

upheavals, and in the central Kanto Plain, rather stable tectonically. On the basis cf

these stratigraphical data, they discuss, in this paper, the processes of the Jomon

Transgression and its environments, Ievels of the shoreline and its deformation, and sea-

level changes in Holocene time, in the whole area of the Kanto Plain.

**

Proceedings

University,

Department l 56, Japan.

of the Institute of

Earth Sciences, No.

of Earth Sciences,

Natural

17, p.

Nihon

Sciences. College of Humanities and

l-16, March, 1982.

University ; Sakurajousui 3-25-40,

-1-

Sciences,

Setagaya,

Nihon

Tokyo,

Proceedmgs　of　the　Institute　of　Natural　Sciences（1982）

織勤惣

滲R，Sσ9αmiOiso

　S∂9∂m’　　　β∂y

a。

　　論kyo　　驚クR．ArqChlb。

　　　R．Tqmo

野號・

5101520km

午　　　　　　　　□1

ρ8σi”σ　　oσθaη吻2

　　　　　　　　醗ヨ3

ChOshi

Kq

Kb

K

b．

H

KC　　　F

　　　　ED

c

Fgi。1　Map　showing　the　invest玉gated　areas

　　a．　Distribut圭on　of　the　alluvial　plains　in　the　Iくanto　Plain

　　b．　Investigated　areas

　　　　A：Paleo－OshikiriBay，B＝Paleo－OfunaBay，CIPaleo－TateyamaBay，D：Paleo・Sanuki　　　　Bay，E：Paleo－lsumi　Bay，F二Tsubaki－umi　Lowland，G：Tama　River　Lowland・H；Area

　　　　around　Tokyo　Bay，1：Tokyo　Lowland，J二〇ku－Tokyo　Bay（Ja：Ara　River　Lowland，

　　　　Jb；Naka　River　Lowland），K：Paleo－Kinu　Bay（Ka：Kokai　River　Lowland，Kb：Sakura

　　　　River　Lowland，Kc：Tega－numa　and　Inba・numa　Lowland）　　　　1．alluvial　plain（includlng　Holocene　terraces）2・terraces　and　hills3・mountain　Iands

2．　Outlines　of　the　stratigTaphy

　　Drowned　valley丘11ings　in　the　Kanto　Plain　have　been　investigated　by　many　geologists

and　geomorphologists（OTsuKA，19341SuGIMuRA　and　NARusE，1954－551HAToRI　et

＆1．，196211KEDA，19641AoKI　and　SHIBAsAKI，19661KAlzuKAαnd　MORIYAMA，19691

NIIGATA　QuATERNARY　REsEARcH　GRoup，19721MATsuDA，1973and1974）．Among

them，SHIBAsAKI，AoKI　and　KuwANo（1971）studied　the　stratigraphy　in　the　Tokyo

Lowland　using　a　great　number　of　borehole　records，and　proposed且rst　that　the　drowned

valley　deposits　are　divided　into　two　formations，the　lower　the　Nanagochi　Formation　of

2

Holocene Stratigraphy and Paleoenvironments in the Kanto Plain

Table 1. Correlation table of the Latest Pleistocene and the Holocene stratigraphy in the

Kanto Plain. figures : 14C age, lvl : marine facies. F : f.uvial Lacies, UA : upper alluvial deposits,

US : upper sand, UC : upper clay, MS : middle sand, LC : Iower clay, LS : Iower

sand. 1) : ENDO, SEKIMOTO and TSUJI (1979), 2) : SEKIMOTO and ENDO (1980), 3) : SHIBASAKI, AOKI and KUWANO (1971), 4) : KAIZUKA, NARUSE and

MATSUDA (1977).

the latest Pleistocene, and the upper the Yurakucho Formation of Holocene time. They,

also, mentioned that there exists a unconformity which is shown by the presence of a

valley (Prehoreal valley) between two formations. Moreover, the ages of a peaty silt

layer overlying directly the unconformity were dated by i4C method to 9,820 ~ 230 y. BP

(GaK-1936) and 9,500~-~60 y. BP (GaK-1937). Lately. KAIZUKA, NARUSE and MATSUDA

(1977) summarized these formations and buried topographies in and around Tokyo Bay,

using borehole data P t' I I basal gravel bed (BG) of the drowned valley was . ar rcu ar y, a

clearly reccnstructed as a channel floor of the Paleo-Tokyo River over the area. Thus,

the area in and around Tokyo Bay including the Tokyo Lowland is where the most

abundant informations have been accumulated.

During the last ten years, on the other hand, small drowned valley fillings in the

southern Kanto Plain have been studied vigorously. This area is characterized by active

upheavals and rich in cutcrops of fossiliferous valley fillings. Especially, based on the

molluscan, foraminiferal, and pollen assemblages and a great number of 14C dates, the

-3~

Proceedings of the Institute of Natural Sciences (1982)

detailed Holocene stratigraphy is established and tectonics, climatic changes and sea level

changes have been also investigated (Paleo-Ofuna Bay : MATSUSHIMA and OHSHIMA,

1974 ; Paleo-Tateyama Bay : YONEKURA, 1975 ; YOKOTA, 1978 ; MATSUSHIMA, 1979 ;

NAKATA et al., 1980 ; Paleo-Oshikiri Bay : YONEKURA et al. 1968 ; ENDO et al., 1979 ;

MATSUSHIMA,1979 ; SEKIMOTO and ENDo, 1980 ; Sanuki Bay : ENDO and SEKIMOTO,

1981 ; Paleo-Isumi Bay: SEKIMOTO and ENDo, in preparation ; Tsubakiumi Lowland : TSUJI

and SUZUKI, 1979).

In Paleo-Oshikiri Bay, the Shimobara Formation equivalent to the Yurakucho For-

mation is divided into two members. Lower one, Kawaa Member, is mainly composed

of manne silt wrth sandy gra~el and peaty silt of the basal honzon Its 14C ages range

from 8, 800 to 7, 700 y. BP. This duration is corresponding to that of rapid rising of the

Jomon Transgression. Upper on.e, Obune Member, consists of gravelly sand, marine silt,

marine sand, brackish sandy silt, and fluvial sandy gravel and peaty silt, in ascending

order. Its 14C ages range frcm 7, 600 to 6, OCO y. BP. This duration is corresponding to

l{]

~ 30 K.~a .e 20 10

O

-]O - 20

- 30

- 40

- 50

- 60

- 70

- 80

- 90

O 20krn 10

Fig. 2

NiizoF.

Toda F.

BG

Longitudinal geologic section along the Ara River and Kokai River Lowlands (1) : Ara River Lowland (2) : Kokai River Lowland a : marine silt or sand bear-

ing molluscan L0ssils,

b : fresh or brackish water silt or sand, c : fuvial sand

and gravel

m 70

60

50

40

30

20

10

O - lO

- 20

- 30

- 40

- 50

- 60

-70

Shimodate

Ishige

:~:r~~:_ ~:~

~:;h..;L ~ ~f

~_

~ 'is~

Kokaigawa F.

O 20 km lO

Kawachi F.

~

Fuji5hiro F.

r~

~e j

BG.

:i~~.

:-*-~-_s

--1~E

_1~:c'~~

: -~~; {-:~:!~ _ ~~ ~Jt:~*-~- -

' tL~~},~l,;~~

~.~f;i~

le:_:

~S{S

~e}:~ -'sol

}~~_o__~1] -._!~~~

Yawara F.(HBG)

- 4 -


that of the maximum phase of the Transgression. Paleo-Oshikiri Bay emerged about

5, 500 -5, OOO y. BP to form the Holccene highest marine terraces. During late Holocene

time, a few younger marine and fluvial terraces were formed. Lithostratigraphical features

as mentioned above are common throughout tho southem Kanto drowned valleys. In

contrast to those in the southern Kanto Plain and the Tokyo Lowland, stratigraphical

works of the latest Pleistocene and the Holocene in the central and eastern ~(anto Plain

have scarcely done.

The authors obtained about thirty thousands horehole records and several hundreds

boring cores in the central (Oku'Tokyo Bay) and the eastern Kanto Plain (Paleo-Kinu

Bay) in order to clarify the stratigraphy and paleoenvironments during latest Pleistocene

and Holocene time. Furthermore, they attempted to correlate the stratigraphy in the

above-mentioned area with those in the southern Kanto and around Tokyo Bay, and, on

the basis of the above results, to discuss the paleoenvironments and sea level changes in

relation to the tectonics in the whole area 0L the Kanto Plain.

Outlines of the stratigraphy in the central and eastern Kanto Plain are as follows.

a) In Paleo-Kinu Bay, there exists a sand and gravel bed with the 14C ages of 9, OOO

to 11.000 y. BP which divides the drowned valley fillings into two formations. It is

the basal gravel of the Holocene deposits and named HBG.

b) In Oku-Tokyo Bay, a basal sandy gravel or sand bed of the Holocene (HBG) is

also found clearly. Its depth below the surface ranges from 15 meters in the upper

stream area, to 35 meters in the present coastal area as is obvious in Fig. 2.

c) In the both Bays, marine facies of the Holocene deposits are distributed extensively,

but in some places, the upper horizon is cut clearly by fluvial and marshy deposits

dated 3, OOO to 4, OOO y. BP by 14C method.

To summarize these, the stratigraphy of each drowned valley is correlative as shown

in Table 1.

3. Holocene stratigraphy and paleoenvironments from the viewpoint of benthomc

foraminiferal assemblages

In the southern Kanto Plain, Holocene stratigraphy and its environments have becn

discussed on the basis of benthonic foraminiferal assemblages (SEKIMOTO and ENDo,

1980 ; ENDO and SEKIMOTO, 1981). Foraminiferal analyses for a number of boring cores

obtained from the central and the eastern Kanto Plain, have been performed.

In this chapter, comparing with the results and discussion in the southern Kanto

Plain, benthonic foraminiferal assemblages from the central Kanto Plain are examined

~5-


,,,O'.LILP.

2]

o pF d'5a~ o~) t. ,, ::'. .*t"

PF 3peh ,D ,.

,

~. a.5 1 1.5 ~ FN 1lo2

,

o 2 4 6 o 1 2 3 ' FN al02 FN l,,a2 ~-･: FN

t･-*･ : PF

FN: Foramfn,ferat nurpber

PR Ra,,ktonic rat,o

PF I~lL)

O O,5 1 1 J5 2 ,tlO

Fig. 3 Geochronological changes of Fora-miniferal Number (FN) and Plank-

tonic ratio (PF) for the drowned valley deposits in the southern and

the central Kanto Plain.

(1) : Paleo-Isumi Bay (Kuniyoshi Formation)

(2) : Paleo-Sanuki Bay(Yawata For-

mation), after ENDO and SE-KIMOTO (1981)

(3) : Paleo-Oshikiri bay (Shimob-

ara Formation), after SEKIM-OTO and ENDO (1980)

(4) : Ara River Lowland (Toda and Niizo Formations equivalent to

Nanagochi and Yurakucho For-mations)

Age of each sample in Paleo-

Isumi and Paleo-Oshikiri Bays

was determined by 14C dating.

Age in Paleo-Sanuki Bay and Ara River Lowland was extra-polated by 14C dates, Iithostra-

tigraphical correlation and se-

dimentation rate.

stratigraphically, and discussed in relation to the transgression. Boring cores used for the

examples shown in Figs. 3 and 4, are located about 7 km northwest (Loc. 1) and 5 km

north (Loc. 2) of Kawaguchi. Both cores of Locs. I and 2 about 40 m in length, are

composed of sandy silt of the lowest (Tokyo Formation) , gravel and organic matter- and

shell-bearing silt of the lower (Toda F.), shell-bearing silt of the middle (Niizo F.), and

organic matter-bearing sandy deposits of the upper horizon (Hikawa F. ) .

The results of the analyses are summarized as follows.

a. Foraminiferal Number (FN) (Fig. 3) : FN values are the highest in the middle,

very low in the lower and fairly higher in the lowest.

b. Planktonic ratio (PF) : Though the ratio is very low through the cores, it becomes

higher in the middle (Niizo F.).

c. Benthonic foraminiferal assemblage : The assemblage from the lowest h ' ' onzon rs

characterized by dominant occurrences of Ammonia japonica and Buccella frigida

with a considerable occurrence of Ammonia beccarii. Ammonia japonica characteri-

stically occurs in bay center to bay mouth (MATOBA, 1970) and Buccella frigida

is important species of thanatocoenosis in northern Japanese open coast and inner bay

such as off Hokkaido (ISHIWADA, 1964) and Matsushima bay (MATOBA, 1970).

Dominant species from the lower (Toda F.) are Ammonia beccarii and Crtbrononlon

- 6 -


o

5

10

15

E

, * aa, 20

a

25

30

35

40

Loc.1 Loc. 2

Fig. 4

IE

ID

IC

･B

IA

~Dlm} toil

~} silt

~1 sand

~] 9ravel

I peat ~l or9inlc materl81

~] 'hell

O '20 e 2o*10 'ro-5 t5-2 02-1 0'1rlh'

Foraminiferal asserrrblages from the drowned valley deposits in the Ara River Lowland

and the columnar sections showing the sampling horizons.

Loc. I : 7 km NNW of Kawaguchi, Loc. 2 : 5 km N of Kawaguchi. T : Tokyo Formation, N : Toda Formation (Nanagochi Formation), Y : Niizo Forma-

tion (Yurakucho Formation), H : Hikawa Formation.

somaense, accompanying Cribrononion cf. subgranulosum or Nonionella stella as subdo-

minant species. Those species are found commonly innermost hay to bay center environment.

Thus, in contrast of the Tokyo Formation, the Toda Formation was characterized by

dominance of mesohaline water and remarkably inner bay environment.

The middle (Niizo F. ) contains dominant species of Cribrononion cf, subgranulosum,

Quinqueloculina spp., and/or Cribrononion sovraense and subdominant species of Crib-

rononion advenum or Ammonia beccarii. Similar assemblages have been reported in

many recent inner bays, Hamana Lake (ISHIWADA, 1958 ; IKEYA, 1977) and other

Japanese bays (UJIIE~ and KUSUKAWA, 1969 ; MATOBA, 1970 ; et al.). Furthermore,

Holocene marine deposits of Paleo-Oshikiri Bay (SEKIMOTO and ENDO, 1980) and the

- 7 -


Tokyo Lowland (UJIl~, 1962, 1963) in the Kanto Plain and Osaka Plain (NAKASEKO

and CHIJI 1956), yield also similar foraminiferal assemblages. All these assemblages

indicate middle to innermost bay environments. Facies of the upper Niizo Formation

become sandy, and this horizon is characterized by abundant occurrence of Quinqueloculina

spp. and common occurrence of Cibicides spp. On the other hand, Upper Kuniyoshi and

upper Yawata Formations in southern Kanto Plain, are dominated by sandy facies, having

Cibicides spp., Elphidiul71 crispwn and Rosalina spp. as dominant or characteristic species

(SEKIMOTO and ENno, in preparation ; EN'Do and SEKIMOTO, 1981).

As described above, each horizon of Loc. I and 2 has peculiar character in fossil

foraminiferal assemblages. It is summarized as follows ;

(1) Tokyo Formation : Iess abundant in FN, open coast to bay center assemblage,

occurrence of cold water species.

(2) Toda Formation : FN values are smallest among four formations, innermost to

middle bay environment.

(3) Niizo Formation : characterized by highest FN, values, occurrence of planktonic

foraminifera, high species diversity, middle to innermost bay environment, upper

horizon is subdominated by assemblage prefering to sandy bottom.

(4) Hikawa Formation : no foraminifers, rich in organic matter, often intercalated by

peaty silt.

These features are recognized also in the other valley fillings of the Kanto Plain and

are useful for determining stratigraphic division of boring cores.

4. Paleoenvironments and Jomon Transgression

On the basis of the Holocene stratigr'aphical data as mentioned precedingly, positional

changes of the shoreline during the Jom-on Transgression and environments of each

phase of the Transgression have been elucidated in the whole area of the Kanto Plain.

The Jomon Transgression ranges in age from 9, 500-10,000 to about 5, OOO y. BP.

T1le earlier half of the duration is characterized by rapid rising of the sea level, and the

later half by gradual rising and the high stand of sea level. And finally it was replaced

by small regression about 5, OOO y. BP.

Distribution of marine or non-marine sediment during the Jomon Transgression in

the Kanto Plain is shown in Fig. 5. A solid circle in Fig. 5 means the locality where

the presence of marine horizon in the valley flllings formed during the Jomon Transgres-

sion is reco*'nized. An asterisk means the locality where only non-marine horizon (peat,

peaty silt, fluvial gravel, etc.) exists. The presence of marine horizon vvas partially

-8-


recognized by direct observation of marine molluscan fossils at outcrops and for core

samples, and by foraminiferal analyses for core samples. In many cases, however, it was

done by interpretation of borehole records. In any rate, Fig. 5 shows generally the

distribution of land and sea around the maximum phase of the Jomon Transgression in

the Kanto Plain.

Preceding the Transgression, fluvial deposits of HBG advanced downwards about

9, 500 to 11,000 y. BP. Their facies vary from gravelly in the upper stream to organic

matter-bearing sand or sandy silt in the lowest stream.

Following their advancing, sea water invaded into the present lowland area, in

resulting that the Tokyo Lowland was already submerged 9, OOO to 9, 500 y. BP. This is

contrary to the archaeological view that the lowland area had not been submerged yet at

~~:Itt~,rl; Y~Hi U~1t~/ ~ ~! ~

t t,rS/i~; t ~~~

~1 -1; ~lt:$r "' ' ~ ~)

~'

･i~"~" ~ . p

'~)~~1~:~¥ te e 'l Totya ely I plcl'lc oc"n

,..

slaami Bay ¥

lk2

Fig. 5 Map showing the distribution for the presence of marine or

non-marine horizon during the period of the Jomon Trans-

gression' Illustrated using the data partly from WAJIMA et

al. (1968), MATSUSHIMA and OHSHIMA (1974), MATSU-SHIMA (1979), and NAKATA et al. (1980). l : marine, 2 : non-marine.

9-

Proceedings of the Instltute of Natural Sciences (1982)

that time (ESAKA, 1972).

Deduced shorelines in 8. OO0-8, 500 and 6, OO0-7, OOO y. BP. are shown in Fig. 6.

In the former duration, sea level was rising rapidly and reached to - 4- - 12 meters above

sea level. Horizontally the shorelines in the drowned valley moved generally inwards up

to near the maximum positions. In Paleo-Kinu Bay, the shoreline of this duration attained

to the innermost position through the transgression.

In the latter duration, sea level, in general, rose up to 2 or 3 meters above sea

level, sea water invaded into numerous small tributaries of the bay, and the shoreline was

situated at the innermost part of the bay, ¥vith a exception of Paleo-Kinu Bay where

fuvial action was dominated. Fig. 6-b resembles the shoreline map reconstructed by the

distributicn of shell middens of the early Jomon Cultural Period (ESAKA, 1972).

~ (~¥)¥ ~1'~ ¥

~L~¥ I~l 11 ~b*.

' '~'-') ¥ l . . .. . ¥~ i¥~~:L~ ~ ¥ I~l ¥,L ¥~~~¥sa~¥ ID~dF'I~;' ,~

/ 1/'v~~ ' ':~:¥ '-' / 1 ~¥' $~~~~~:~¥

~~~~:~ fl' 1 ~ l' f': --;'~ "'¥", l'¥"¥.'t t' ~'/(:~'¥~ . ,,.-..¥ ( ;" ' . /~¥ ll f ¥ !n ' ~ s~~J'~~:>) -s /

~?~ ~ " ~~:!d~;:¥¥;PI~ L / ~s

~ "-~ ~. ~r

O 10 20km

~~'~~~~b ~~~~¥:~~¥~~r~¥1 ~~~iij~;~:~:' ¥'v'~ ~"

~ ' L'~~!~~:.;~:~:~:)~~;:¥~..~~~:~i":¥~~<~~~~~~~~:~;: !¥'~ ~~a¥'~~~~

"¥¥C)~:~

~,_ , ** ~;s ~1~ / " C~:~* .' ~ ' I~"s~~~¥/;;~~~ ~

~{ l-~ ~¥Jvv ' !-:t~- 2~~

~_'~~

O 10 20km

Fig. 6 Map showing the shoreline during the Jomon Transgression in the Kanto Plain. Illustrated using the data partly from KAIZUKA and MORlYAMA (1969), MATSU-SHIMA and OHSHIMA (1974), KAIZUKA et al. (1977), MATSUSHIMA (1979), ENDO et al. (1979), NAKATA et al. (1980), and ENDO and SEKIMOTO (1981). a : Shoreline during 8, OOO-8, 500 y. BP

b : Shoreline during 6, OO0-7, OOO y. BP

Dashed lines show former shoreline.

- 10 -


5. Displacements of the shore levels and sea level changes in Holocene time

t r'n horizon in each bore hole Fig. 7 shows altitudinal distribution for the highes ma I e

and outcrop of the Holocene deposit in the Kanto Plain. This horizon is approximately

f the Jomon Transgression, 5, 500 to 6, 500 y. BP. corresponding to the maximum phase o The altitude depends originally on the highest level of the Jomon Transgression with a

small discrepancy due to the situation in the bay, beach, river mouth, bay center, etc.

It has been deformed during the last 6, OOO years, 110wever, by crustal movement, trunca-

tion of fluvial processes, and recent land subsidence. In the southern Kanto Plain, it is

very clear in Fig. 7 that the nearer the Sagami Tectonic Line situated southwest of the

Kanto Plain, the higher the altitude of the highest marine horizon becomes. This active

tilting is attributed to the frequent seismic upheavals such as associated with 1923 Kanto

Earthquake (SUGIMURA and NARUSE, 1955 ; YONEKURA et al., 1968 : YONEKURA., 1975 ;

2.5

~;

~

s~~. _ ¥ 2.5

,.~ ... I ~'~vrfT 5

p 2,e

2o ¥ '. a5¥¥¥ ~-* 12.' 1¥¥ ¥ ¥ ¥¥ '~ .

¥ ¥ 17.e 2o km 10 ¥

¥ 22.5 ¥

Fig. 7 Altitudinal distribution of the highest marine horizon during

the maximum phase of the Jomon Transgression

- 11 -

1嵩

｝

11》

30m

0

　ロじ　　　　　　　　　　　　　　　　　　　　　　　　　　び　　　　　　　　　　　　　　　　　　　19　　　　　　　　　　　　　　1。’．

ジノ～、

一50

　　m　30

30

0

m

b．

、

一50

121

0

30

α．

　　　　　　　　　　ノ　一一－　　　　　　●も●7●6●o

圃50

拠

、、

　恥　《3｝

30

0

一50

ム　　あ

0

“

ム1

▲2

●3

●

● ●

A　6

、￥

　　o

　而　14130

、

＼

一50

0

o

5 　　　　　　ヘロ×103y．B．P．

一50

●

＊1

＊2

＊3

＊4

’u嬬一

ゆ

　　　　　　　　　5　　　　10　　　　　　　　　5　　　　コ0　　　　0　　　　　5　　　　　　　　　　　　　　×103y・B・P・　　　　　　　　×1・3y・B・P・　　　　　　　　　×103y．B．P．

　　　　　　　　　　　　　　　　Fig。8　Shore　level　displacement　curves　aud　revised　sea　Ievel　change　curves

　　　　　　　　　　（1）：Paleo－Oshikiri　Bay，（1）一a：Shore　level　d藍splacement　curve，（1）一b　l　Revised　curve．＊1

　　　　　　　　　　（2）＝Paleo・lsumi　Bay・（2）一a：Shore　level　displacement　curve，（2）一b：Revised　curve．＊2

　　　　　　　　　　（3）：Shore　Ievel　displacement　curve　in　Paleo・Kinu　Bay．＊3

　　　　　　　　　　（4）：Shore　level　displacement　curve　around　the　Tokyo　Low豆and．＊4

　　　　　　　　　　　1：peat　and　wood　from　non－marine　deposits，2：wood　and　peaty　silt　from　marine　and　　　　　　　　　　　brackish　deposits，3；molluscan　shell　from　marine　deposits。

IIlustrated　using　the　data　partly　from　YoNEKuRA　et　aL（1969）and　ENDO　et　aL（1979）．

IIlustratedusingthedatapardyfr・mOHARAandTAIRA（1974），NIRElandYADA（1977），andNAGAsAwA（1979）．Illustrated　using　the　data　partly　from　OYA（1969）．

Illustratedusingthedatamainlyfr・mMATsusHIMA（1976and1981），KAlzuKAetal．（1977），andUMITsu（1977）．

10

℃『

oo①oαb的

o

げo

口

oΦ

亀

z象

同m

ωoΦ口

oΦ

oGO腫）


NAKATA et al., 1980).

On the other hand, in the central Kanto Plain, the altitude seems to be rather

constant, around 2.5 meters ahove sea level. At the same time, it shows a small and

10cal variation ranging from 3 to - O. 5 meters. There is, however, no regional trend such

as upheaving unidirectionally towards the south, the north, or the center. A few local

center showing low value are situated near Kazo, in the central Kanto Plain, around

Tokyo Bay and the Tokyo Delta, and along the Ara River. These are corresponding to

the land subsidence centers in recent ages. Consequently, from the viewpoint of subsurface

geology and geomorphology, the central Kanto Plain has not been effected by tilting

having been active in the southern Kanto Plain.

In Fig. 8, shore level displacement curves in Holocene time are shown. Broken

lines in Figs. 8-(1) and (2) mean average upheaving rate which is based on the following

assumptions.

(1) Sea level about 6. OOO years BP reached to 3 meters ahove sea level which are

common level of the highest marine hcrizcn in the central Kanto Plain.

(2) Seismic upheaving rate has been approximately uniform throughout Holocene time.

Figs. 8-(1)b and (2)b show curves revised by each average upheaving rate. These

revised curves are similar to the shore level curves as shown in Figs. 8-(3) and (4). It

suggests that the revised curves [8-(1)b and (2)b] or the shore level cuves [8-(3) and (4)]

indicate sea level change curves (eustatic curve) , to first approximation, if some regional

tectonic movement can be neglected.

6. Concluding Remarks

Drowned valley deposits of the latest Quaternary, distributed along the main rivers

and their tributaries in the Kanto Plain are divided into two. The both units of the

lower and the upper, having gravel to gravelly sand bed in their basal horizon, are cor-

related with the Nanagochi Formation of the latest Pleistocene and the Yurakucho For-

mation of the early to middle Holocene in the Tokyo Lowland (SHIBASAKI, AOKI and

KuwANO, 1971), respectively.

Foraminiferal assemblages from the Nanagochi and the Yurakucho equivalent forma-

tions show commonly inner bay environments, ranging from bay center to innermost

bay. Reflecting advancement of the Jomon Transgression, values of Foraminiferal Number

and planktonic ratio are increasing in the Yurakucho equivalent formations.

The highest level of the sea attained to 2-3 meters above sea level about 6, OOO-

6, 500 y. BP in the central portion where the seismic upheaval is negligible. Jomon

- 13 -

Proceedings　of　the　Inst…tute　of　Natural　Sciences（1982）

shorelines　during　the　early　and　the　maximum　phase　of　the　Jomon　Transgresslon　were

reconstructed　mainly　on　the　bas1s　of　borehole　data．Those　indicate　that　in　early　Ho1㏄ene

age，the　shoreline　was　situated　nearly　in　the　imermost　portion　of　the　drowned　valley，

　　　Revised　shore　level　displacement　curves　of　the　southern　Kanto　are　similar　to　the

shore　level　displacement　curves　of　the　central　and　eastem　Kanto　Plain．It　suggests　th＆t

the　revised　curves　approximate　the　sea　level　change　curve．

Referenees

AOKI・S・and　SHIBAsAKI，T，（1966）Problems　on　the　lithological　facies　and　subdivision　on　the

　　　　so・called　alluvial　marine　deposits　in　Japan．The　Quatemary　Research（Japan），voL5，P．

　　　　113－120（in　Japanese　with　Enghs猛abstract）．

ENDO・K・SEKIMOTO，K　and　TSUJI，S、（1979）Holocene　stratigraphy　and　paleoenvironments

　　　　in　the　lowland　along　the　River　Nakamura，southwestem　Oiso　Hills・Kanagawa　Prefecture．

　　　　Proc，Inst．Nat，Sci，，Nihon　Univ，，no．14，p．9－30（in　J　with　E）．

ENDo・K　and　SEKIMoTo，K（1981）Holocene　stratigraphy　in　the　coastal　area　of　Sanuki－machi，

　　　　Chiba　Prefecture，Japan・Proc．Inst，Nat，Sci．，Nihon　Univ．，no。16，P．1－11（in　J　with　E）．

EsAKA・T・（1972）Change　of　natural　environment　during　the　Jomon　Cultural　age．The　Quatemary

　　　　Research（Japan），voL11，p・135－141（in　J　with　E）．

HAToRIラKヲINOKucHI，M・，KAlzuKA，S．，NARusE，Y．，SuGIMuRA，A．and　ToYA，H．（1962）

　　　　Latest　Quatemary　features　of　Tokyo　Bay　and　its　environs．The　Quatemary　Research（Japan），

　　　　vo1・2，P。69－90（in　J　with　E）．

IKEDA・T・（1964）Study　on　the　Alluvial　Deposits　of　the　Tokaido　Region。lns．Geo1．Paleont、

　　　　Tohoku　Univ，no．60，85p．（in　J　with　E）．

IKEYA，N、（1977）Ecology　of　Foraminifera　in　the　Hamana　Lake　Region　on　the　Paci且c　Coast　of

　　　　Japan、Rep。Fac．Sci．，Shizuoka　Univ．，voL11，p．131－159．

IsHlwADA，Y。（1958）Studies　on　the　Brackish　Water，part　III♂Recent　Foraminifera　from　the

　　　　Brackish　Lake　Hamana－ko一，GeoL　Surv，Japan，Rep．，no．180，11p．（in　J　with　E）．

IsHlwADA・Y・（1964）Benthonic　Foraminifera　off　the　Paci且c　Coast　of　Japan　referred　to　Biostra・

　　　　tigraphy　of　the　Kazusa　group．GeoL　Surv．Japan，Rep．，no．205，45p．

KAlzuKA，S・and　MoRIYAMA，A．（1969）Geomorphology　and　subsurface　geology　of　the　alluvial

　　　　pla三n　of　the　Iower　Sagami　River，Central　Japan。Geograpica正Review　of　Japan，voL42，

　　　　p．85－105（in　J　with　E）．

KAlzUKA，S・，NARUSE，Y．and　MATSUDA，1．（1977）Recent　Formations　and　Their　Basal

　　　　Topography　in　and　around　Tokyo　Bay，Central　Japan．Quatemary　Research，voL8，P．32

　　　　－50．

MAToBA，Y。（1970）Distribution　of　Recent　Shallow　Water　Foraminifera　of　Matsushima　Bay，

　　　　Miyagi　Prefecture，Northeast　Japan。Sci．Rep．Tohoku　Univ．，2nd　ser．（Geo1．），voL42，

　　　　p．1－85．

MATsuDA，1，（1974）Distribution　of　the　Recent　deposits　and　buried　landforms　in　the　K＆nto

　　　　Lowland｝central　Japan。Geograp。Rep，Tokyo　Metropohtan　Univ．，vo1．9，p，1－36．

MATsusHIMA，Y。（1976）The　a至1uvial　deposits　in　the　southem　part　of　the　Miura　Peninsula，

　　　　Kanagawa　Prefecture。Bu1L　Kanagawa　Pref．Mus．，voL9，p．87－162（in　J　with　E）．

一14一

Holocene　Stratigraphy　and　Paleoenvironments　in　the　Kanto　Plain

MATsusH正MA，Y。（1979）Littoral　Molluscan　assemblages　during　the　Postg豆acial　Jomon　Trans－

　　　　gression　in　the　Southem　Kanto，Japan，The　Quatemary　Research（Japan），voL17，p，243

　　　　－265（in　J　with　E），

MATsusHIMA，Y。and　OHsHIMA，K（1974）Littoral　molluscan　fauna　of　the　Holocene　Chmatic

　　　　Optimum（5，000－6，000y．BP）in　Japan，The　Quatemary　Research　（Japan），voL13，p．

　　　　135－159（in　J　with　E）．

NAKAsEKo，K．and　CHIJI，M．（1956）On　the　fossil　foraminifera　in　the　subsurface　sediments　in

　　　　Osaka　City　and孟ts　suburbs，North　and　South　Colleges，Osaka　Univ，，ScL　Rep，，no．5，p，

　　　　43－71（in　J　with　E），

NAKATA，T，，KoBA，M．，IMAlzuMI，T．，Jo，W．R．，MATsuMoTo，H．and　SuGANuMA，T，　　　　（1980）Holocene　marine　terraces　and　seismic　crustal　movements　in　the　southem　part　of

　　　　Boso　Peninsula，Kanto，Japan．Geographical　Review　of　Japan，voL53，p，29－44（in　J

　　　　with　E）．

NIIGATA　QuATERNARY　REsEARc｝王　GRouP　（1972）　Studies　on　the　biostratigraphic　division

　　　　and　the　sedimentary　environments　of　the　Alluvium　in　the　Tokyo正owland　and　Niigata

　　　　Plain，Central　Japan．In“Coastal　Plains　of　Japan”（T．UTAsHIRo，ed），The　Mem・GeoL

　　　　Soc．Japan，no・7，pp・213－233（in　J　with　E）・

OHARA，S，and　TAIRA，K．（1974）MoUuscan　Remains　from　the　Taito－zaki　Formatlon・Jour・

　　　　Co1L　Arts　Sci．Chiba　unlv．，B－7，p．43－59．

OTsuKA，Y．（1934）Physiograpy　of　Tokyo　during　late　Quatemary，Proc，Imp・Acad・シvoL10，

　　　　p，274－277，

OYA，M．（1969）Geomorphology　and　Flooding　of　the　Plain　in　Middle　and　Lower　Reaches　of

　　　　the　Tone　River　in　Kanto　Plain．Jour，Geography，voL78，P．341－354（in　J　with　E）・

SEKIMoTO，K．and　ENDO，K．（1980）Foraminiferal　Assemblages　and　Paleoenvironments　o｛the

　　　　Holocene　Shimobara　Formation　along　the　Lower　Reaches　of　tke　River　Nakamura，Kanagawa

　　　　Prefecture，Japan．Proc．Inst、Nat．Sci．，Nihon　Univ．，no．15，P、19－32・

SHIBAsAKI，T．，AoKI，S．and　KUwANo，Y。（1971）Signi丘cance　of　Buried　Valleys　and　Other

　　　　Topographies　in　Elucidating　the　Late　Quatemary　Geohistory　of　Japanese　Coastal　Plains・

　　　　Quatemaria，voL14，p．217－236．

SuGIMuRA，A．and　NARusE，Y、（1954－1955）Changes　in　sea　leve1，seismic　upheavals　and

　　　　coastal　terraces　in　the　southem　Kanto　region，Japan。Japan．JouL　Geol・GeogL　vol・24シ

　　　　P．101－113；voL　25，P、165－176。

TsuJI，S．and　SuzuKI，S．（1977）Pollen　Analysis　of　the　Holocene　Higata　Formation孟n　the

　　　　North　of　t｝1e　Kujukuri　Coastal　Plain，Chiba　Prefecture，Japan，The　Quatemary　Research

　　　　（Japan），voL16，p・1－12（in　J　with　E）・

UJII亘，H．（1962）Introduction　to　statistical　foraminiferal　zonation，Jour．GeoL　SocJapan，voL

　　　　68，　p、431－450、

UJIIE，H．（1963）Foraminifera　from　the　Yurakucho　Formation（Holocene），Tokyo　City．Sci．

　　　　Rep．，Tokyo　Un三v．Educ．（Tokyo　Kyoiku　Daigaku），sec，C，no。79，p．27－4L

WAIIMA，S．，MATSul，T．，HAsEGAwA，Y．，OKAMOTo，L，TSuKADA，K，TANAKA・Y・夕　　　　NAKAMuRA，Y。，KoMIYA，T．，KuRoBE，T．，TAKAHAsHI，K．and　SATo，T・（1968）On－

　　　　the　Highest　Sea　Level　of　the　Neohth重c　Transgression　in　the　Kanto　Plain・Misc・Rep・Res・

　　　　Inst．Natur．Resources，no．70，p．108－129（in　J　with　E），

YoNEKuRA，N．（1975）Quatemary　tectonic　movements　in　the　outer　arc　of　Southwest　Japan

一15一

Proceedings　of　the　Institute　of　Natural　Sciences（1982）

　　　　with　special　reference　to　seismic　crustal　deformations．BulL　Dept・Geograph・・Univ・Tokyo・

　　　　no．7，P．19－71．

『YoNEKuRA，N．，SuzUKI，1，，HAsEGAwA，M．，UEsuGI，Y・，ENDo，K・OKADA・A・・KAwANA・

　　　　T．，ISHIKAWA，K，and　FUKUDA，M．（1968）Radiocarbon　Dates　and　HQlocene　Marine

　　　　Terraces　along　the　Coast　of　the　Bay　of　Sagami，Central　Japan．The　Quatemary　Research

　　　　（Japan），voL7，p・47－55（in　J　with　E）・

16一

hoiocene stratigraphy and paleoenvironments in …...the authors have investigated the stratigraphy...

Documents