itamii lierrace - osaka city...

1ournal of Geosciences， Osaka CIty UnIve:r;sIty Vo1. 14， Art. 3， p. 53-70 March 1971

Itamii lierrace

Ylitlh， Spec'ia:11 ，Reference tO. th，e Late

Pleistoc，ene Transgression， i:n: Japan*

Kazuo H~JZ[TA and Yasuo MAEDA

(with 6 Tables and 10 Figures)

Contents

Introduction

Topographic features of the Itami area

Subsurface geol<ogy of the Itaffili up加ld

Dating of the Itami clay

Pa;Ieoenvironments o{ the Itami formation

Tectomic situation of the Itami basin

Significance of the Itami transgression

Swnrnary

Introduc“on Although only fragmentary data have been announoed on the transgression of the

Late Pleistocene in Japan， the authors emphasize here that the Itami area， northwest of

Osaka (Loc. 7 in Fig. 8)， is one of the best localities to observe the marine clay of that

time at the ，c1iffs along the terrace scarps owing to the extraordinary upheaval of the fault

block. Most of such clays are considered to be hidden beneath coastal plains.

At first， ITIHARA described the Itami gravel as the deposits of the regressive stage of

Osaka Bay (IT:tHARA， 1960)， but OKA (1963) found 0凶 atrun marine clay intercalated

within this thick gravel bed at Kamikushiro and designated it as Itami clay. The authors

have carried out intensive survey of this clay since 1965 and have tried to clarify the sig圃

nificance of the transgression of the Itami clay from various points of view. Among them， palynological study has already been pubHshed by恥1AEDA(1970). The descriptions on

the topographic surfaces of the Itami area given in the “Land condition map of the Osaka

Plain" (Geographical Survey Institute， 1965) have been very suggestive to this work.

The authors express their sincere thanks to Prof. M. SHlMAKURA for his advices on

pollen analysis， to Prof. K. KIGOSHI for dating， to Dr. S. KANEKO for identification of

molluscan fossils， to Dr. M. CHIn for foraminifera， to Y. NOGUCHI for diatom， to R. B. TATE

for his help given to their surveys in Burnei， to Dr. S. KOKAWA， Dr. H. MACHIDA and

N. HORI for their 0仔ersof unpublished data. Thanks are also due to Dr. T. KASAMA

* Contribution from the Department of Geosciences， No. 225

、

54 Kazuo HUZITA and Yasuo MABDA ，

for his contineous encouragement， to Mrs. T. Y AMAUCHI for her assistance in laboratory

and to the authorities of Itami City for the helps during this work.

Topographic features of the Itami area

The Italni area is a small basin of quadrate-shape surrounded by mountain lands， Hokusetsu on the northern side， Rokko on the western side， by Senri hilly land on the

eastern side， and opening towards the Bay of Osaka on the south (Fig. 6). Especially the

Rokko range rises more than 900 m fron1 the Itami basin showing steep fault scarps on

its southeastern side (Pl. 1 in HUZITA et al.， 1971， of this volume).

The Itami area is drained by two main rivers， the R. Muko on the west and the R. Ina

on the east. Various terraces are distributed along and between these rivers. They are

divisible into middle and lower terraces. The higher terraces are on1y scattered at a hight

of more than 200 m along the fault scarps of the Rokko independently from the topo-

graphic shape of the Itami basin. The middle terraces develop around the mountain

foot， while the lower， named Itami terrace， is widespread on the bottom of the basin

(Fig. 1).

Although the northern highest part of the Itami terrace reaches more than' 40 m， it

gent1y inclines southwards to Osaka Bay and is covered with alluvial deposits in Amagasaki

coastal plain. The sonic survey of Osaka Bay with SPARKER in 1963 revealed the former

river channels on the extension of the Itami surface which have been buried under the

unconsolidated sediments in Osaka Bay (HUZITA， 1966， 1969; HUZITA & MAEDA， 1969). They indicate the large regression antecedent to the I-Iolocene transgression.

As、shownin Fig. 1， the Itami terrace is composed of various surfaces slightly different

in altitude. The distribution of them clearly shows that the Itami terrace is made of two

big fans which have been developed at the mouths of the older R. Ina and R. Muko flowing

into the Itami basin.

At that time， the R. Muko might have run more eastern course than the present and

joined with the R. Ina in the central part of the basin. Then， the R. Muko has changed

its course gently to the west fOflDling minor terraces， while the R. Ina has dissected its own

fan straightly in the central part and has lnade distinct scarps along the eastern side of

the terrace. Such change of the river courses is inferred to be due to the westwards tilting

movement of the fault block cut by t1ae hidden fault extending along the R. Muko and

R. Ina (HUZITA et al.， 1971). The tributaries from the northern Hokusetsu mountain land

have also made small fans in the lower part between two big fans.

Former stream channels can be traced by aerial photographs on the terrace surface

showing their changing courses. They are cut by topographic lineaments almost paral1el

each other. The one is a fault scarplet running in ENE-WSW direction. The other is a

forrow cutting the terrace. Although the former stfeam channels on the terrace can be

traced strightly across this furrow， the present ones change their courses to the east or

west along it. A big pond named Koya-ike was constructed utilizing this furrow about

1，200 years ago.

•

N

仁コ1

匡ヨ 2

で~3

Eヨ4

NISHINOMIYA

5 阻圃 6

。 2 3

Itami Terrace

阜、{OOO

4 km OSAKA

Fig. 1 Distribution of the terraces in and around the Itami basin. 1. Alluvial plain: 2. Ikeda terrace; 3. Itami (lower) terrace; 4. Uegahara (middle)旬rrace;5. Gokayama (higher) terrace; 6. Terrace scarp.

55

The Koya..ike furrow clearly extends to the northeast towards the depressonal zone

of the northern side of Senri Hill. Another obscure depression can be recognized along

the foot of the Hokusetsu mountains.

Subsurface geology of the Itami upland

Along the cliffs of the eastern side of the terrace， is exposed the formation comprising

the Itami terrace. The standard profile of it can be established by these outcrops. More

than three hundred dril1 data have been collected and many trenches for constructions

have been observed to confirm the distribution of the Itamifornlation (Fig. 2). The panel-

diagram of Fig. 9 is a summary of the compilation of them.

56 Kazuo HUZITA and Yasuo MAEDA

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Fig. 2 Location map of driI1l points in the Itami area. Solid lines indicate the pro.file lines of the panel-diagJiam in Fig. 9.

ltami Terrace 57

The Itami formation is composed of

Itami gravel and Itami clay showing a

cycle of sedimentation. Cobble-size sub-

angular gravels are abundant in the Itami

gravel. Paleozoic rocks are predominant

in the older fan of the R. Ina， while the

granitic or rhyolitic rocks are dominant

in that of the R. Muko， indicating the

rock bodies exposed along the upper

courses of both rivers.

The Itami ctay is blue in fresh part

but dark gray in weathered part. In the

northern area， it is only lenticular thin

layer intercalated between Itami gravel

and the underlying Kawanishi gravel

which is closely similar to the Itami，

but it becomes thicker increasingly south-

wards as shown in Fig. 10.

The Itami clay yields abundant mol-

luscan fossils in the southern thick parts.

Many sand pipes can be recognized in

the northern lenses. In the northern-

most part， it is very difficult to discrimト

nate the Itami gravel from the Kawanishi

without Itami clay.

U nder the flood plain of the R. Ina，

<0 ， 'L..

C 戸、 1 1， 1， l' 1 ~ o 1 E 11 _ 1: 1. 1 1 ~ 1 <0 '+=i 、~ I! ~ l' Remarks 1 ~ 1 E ・SIo 何-6 li E 1: Hemarl<s 1 c: 1 ~ 1 Eω E Ei コ l ω21~I ~ ~ 11 Q) 11 O li 一=-ωm』o-。-ε 。lυ £百£ 2

sand Sllty claγ

+ 4 。。ーーーーーーーーーー.

向 bble-cobble

一〉ω granlte ~ 1 11 o，"， 0 _ ~I rhyohte c) 1 .u _ v _ v"，: I chert

〈〉。0 。0 sandstone ':;: 1 Sea E oo ωlevel 11 ~ ~~ ~ 1 11 ~ ~'õ'"oO 1 pebble

a・o 0 ・0 0

。b:4・・ chert 。。。・.e ・18

sllt ・171 1 li C: 1 1 -子三三:--~ sllty clay ・16・81 1: o 1 1 11-ー・ "ー・1151 1 " 号 " -7JJ .14・7I 11

E 1 1 IE =="l clay ・113L.. I I __IILー一一一-_ ーー。 -5.00，[-_(; ・12・6 ・5恥・11

ムー molluscan 1 .10・5 ・4E 1 1 11 fosSlls abundant ・9~ 1 >1 I I==~・8 ・4 ・ 3";"'1 <0 . 7

υ ・2

E 1 11 _ 1 1 • 6 jg 一一φ ・31 • 1

• 5 10.00・二・2伊

，ニ二@二二 Slltyclay ・414 1. 1 1: • 31 • l' l' 1 1:

f，"e sand ・2sand ・1

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£ 0 0 0 CC 〉C 王 -g志 00 ・ |ω c: :> 1 11 '"' ;: r¥ 1 1 1 11 1 11 S 11 ~ ~ 1- 11 ~ ~ ~ 1 1 1 l' 1 li gω'1 ~一ら 1500 0 。0〕 0。~ 1 ~ 1 Ilo(..} o-~

Fig. 3 Standard columnar section of the Itami formation at Loc. 10 in Figs. 1 and 2.

it was confirmed by the deep open-cutting for the conststruction of the subway crossing the

Osaka International Airport that the Itami clay had been completely eroded out during

the large regressive stage of the Main Wurm time and that the Ikeda gravel covers directly

the Osaka group (Fig. 9).

A fault was confirmed by two test logs especially carried out for this purpose on both

sides of above-mentioned scarplet traversing the Itami street. The upper surface of the

Itami clay is shifted 8.5 m by this fault at Locs.4 and 5 in Figs. 1， 2 and 10. This Itami

fault is inferred to extend to the west along the southern side of the Uegahara (middle)

terrace. Along the Koya-ike furrow， a fault is also inferred to be as the extension of the

Koyo fault.

Dating of the Itami clay

In 1966， the authors found a wood fragment from the Itami clay at Loc. 2 in Figs. 1， 2

and 10. Abundant fragments of fossil Osfrea were obtained from the test driI1 core of Loc. 5.

The radiocarbone-dates of them by K.IGosm are as follows .

•

、

58

Loc. 2

Loc. 5

Kazuo HUZITA and Yasuo MAEDA

29，800+ 1，200 (Gak 489)

+ 3，300 32，700-2，500(Gak1809)

by wood 34048'20ゲN，135024/48HE

by shell 34046'55ゲN，135025/04ME

Paleoenvironments of the Itami formation

Numerous data concerning the paleoenvironments of the Itami formation were obtained

from the outcrops or drill cores at the localities shown in Fig. 1. Especially， at Loc. 10，

many paleontological data were collected on molluscan shells， diatoms， foraminifers and

pollens. Detail of the columnar section of this point is given in Fig. 3.

Summarizing these results， it is inferred that the Itami clay was deposited during the

transgression in moderate climate， whi1e the Itami gravel was deposited in the regressive

stage in cQoler climate， according to the playno~ogical analysis.

Itami clay

Molluscan fossils studied by KANEKO: Among the species listed in Table 1， Turritella

kurosio IDA is an only extinct specires. All other species are now living in Osaka Bay.

Diatoms studied by NOGUCHI: Also closely related to the diatom assemblage ofpresent

Osaka Bay. The change of diatom assemblages along the sequence clearly reflects the

changing conditions of the standing water (Tables 2 and 3).

Table 11• , List of molIuscan fossi1s of the Itami clay.

Pelecypod Striarca interplicata (KING et GRABAU) Scapharca satowi (DUNKER) Alvenius ojianus (YOKOYAMA) Anodontia stearnsiana UYAMA Pillucina pisidium (DUNKER) HKellia" notoensis (YOKOYAMA) Borniopsis tsurumaru HABE

Gastropod

Sinusicola yendoi (YOKOYA'MA) Turritella kurosio IDA Cerithidea rhizophorarum A. ADAMS Australaba picta (A.ADAMS) Clathrofenella fusuca (A. ADAMS) Euj初ellapupoides (A. ADAMS) Neverita reiniana (DUNKER) Zeuxis succinctus (A. ADAMS) Reticunassa sp. lndomitrella yabei (NOMURA) Babylonia japonica (RBEVE) Sydaphera伊engleriana(DESHAYES) Pseudorhaphitoma sp.

(identified by KANEKO)

Fulvia mutica (REEVE) Paphia undulata (BORN) Dosinella penicillata (REEVE) Raeta rostralis (REEVE) Macoma tokyoensis MAKIYAMA Anisocorbula minuitissima HABE

Etremopa subaulφrmis (SMITH) Amaea thielex (de BOURY) Actaeophyramis pereximia NOMURA Miralda affectuosa (YOKQYAMA) Tiberia fasiata (DUNKER) Syrnola subcinctella NOMURA Iphiana tenuisculpta (LISCHKE) Turbonilla sp. Odostomia sp. Ringicula dorialts GOULD Caleophysis minima (YOKOYAMA) Rhizorus tokunaf?ai (MAKIYAMA) Granuliterebra bathyraphe (S叩 TH)

Itami Terrace

Table 2. List of diatom assemblage of the Itami clay. (identified by NOGUCHI)

Horizon of diatom in Fig. 3 8 7 6 5 4 3 2

A ctinocycJus ehrenbergii 一 I.4 1.4 1.2 2.2 0.3 一一Actinopt)lchus undulata 0.3 一一一一一一一Auliscus caelatus 2.~ 0.6 0.5 2.4 1.1 0.3 一 8.7 Coscinodiscus oculus-iridis 一 0.6 1.1 1.2 一 0.3 一一Cosc. radiatus 1.5 0.6 0.5 1.2 0.4 2.3 3.7 一Cosc. subtilis 一一一一 0.7 一一Cosc. eχcentrtcus 一 0.6 0.5 一一一一 4.4 Cosc. lacustris 0.3

. 一一一一一一一

Cosc. curvatulus 1.5 一一一一一一一Cyclotella striaω 14.9 2.8: 0.9 3..5 5.2 一一一*Cyc. stylorum 4.8 5.6 5.0 3.5 12.2 11.0 一 4.4 Hyalodiscus cf. subtiUs 一 0.31 0.5 一 1.5 一一一凡t[elosira sulca'ω 25.4 76.3 76.0 69.0 51.5 67.5 81.5 13.0 M granulata 1.5 一一一 2.6 一一 8.7' M solidα 1.5 一 t)，.31 2~4 0.7 -ーーー-11 一一Stephanodiscus niagarae 一一一一一一一 4.4 St. •

0.2 0.4 carconens，Ls 一一一一一一Stephanopxis turris 一 0.3 一 .圃E・E・-‘ 0.4 2.3 一一Thalassiosira antiqua 一 0.8 一一一一一一Terpsinoe americana 一一一一 0.7 一一 8.7 Triαrattum favus 一 0.3 一一一一一一Coscinodiscus marginatus 一一一一一 0.3 一一

A chnanthes ，andicola 1.5 一一一一旬開-同-11 一一Coconeis thumen'Sis 2.'9 一一一一一一Diploneis smithii 2.9 0.6 0.9 3.6 2.6 1.2 一 4.4 D'ipl splendrida 1.5 0.3 一一 0.4 t .7 3.7 一目

Dipl mantichora 1.5 0.3 一一一一一一Epithemia turgtda -ーー「 0.3 一一一一一Fragilaria pinnata 1.5 一一一 -・・・・・叫一一一Gornmphonema grevel 1.5 一一一一一一一Grammatophora s:p. 1.5 一 0.5 一 0.4 -ーーー叫一一Navicla contorta (N. raeana) 一 0.4 2.1 3.5 5.5 1.2 一 4.4 N. l'yrα 一 0.8 0，.5 一 0.7 1.2 一 8，.7 N. punctulata 一ーー・『 0.2 一 0.4 一一一N. galikii 1.5 国ー「一一一一一一Nitzschia granulata 1:1.8 0.3 一一一一一一Nitz. plana 一 0.3 0.5 一一一一Nitz. puncutata 一 0.3 一一 1.5 一一一Nitz. cocconiformis 一 4.5 6.1 6.0 7.4 8.7 11.1 30.2 Pleurosigma intermedium 0.3 一一一一一一Surirella fastuosa 1.5 0.8 2.5 1.2 1.1 1.7 一一Thalassionema nitzschioides 16.4 一一一一一一Tracyneis a伊era 一 0.3 0.2 1.2 0.7 一一一Tr. antillarunz 一一 0.2 一 0.4 一一一

Centra:les % • 54.3 90.5 86.9 84.4 79.6 84.3 85.2 52.3 Pennales % 45.7 9.5 13.1 15.6 20.4 15.7 14.8 47.7 Littoral marine plankton 1) 9.O 6.9 9.0 8.5 13.6 8.7 7.4 13.1 Marine benthos 2) 28.3 76.3 76.0 69.0 51.5 67.8 81.5 13.0 Marine Of brackis)a 41.8 13.7 13.4 16.6 25.6 23.5 11.1 60.8 Brackish or fresh 4) 14.9 2.8 0.9 3.5 5.2 一一一Euli，mnoplankton 4.5 一 0.5 2.4 3.7 一一 13.1 Heleoplankton 6) 1.5 0.3 一一一一一一ln brook or stream 7) 一一 0.2 一 0.4 一一一

Tropical species 4.8 6.0 7.1 7.0 10.7 11.2 一 8.8

4)

2)

2)

2)

6)

6)

1) 7)

3)

59

，

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d


Table 3 Paleoenvironment considering from the diatom assenlblage.

Horizon Environment Remarks

ti

今''M今

3

A

U寸

ζJfO弓I

0

0

Initial stage of transgression

Lagoon

Beginning of transgression

Stable inner bay

Same rate of Centrales and Pennales

Rapid inereasing of M elosina sulcata

Coexistence of marine plankton and brackish soecies

Abundant Centrales

Beginning of regression Increasing of Pennales Dcreasing of Centrales

Foraminifera studied by CHI]I: As a whole， species of warm current are abundant， and

the inhabitants of inner bay are predominant. However， it is noticeable that the horizon

No. 3 contains planktonic foraminifera showing the connection with the open sea. The

detailes are given in Table 4.

Table 4. Lilst of ForamiDifera of the Itam1i clay. (identified by Cmn:)

Horizon of Foraminifera Species

2 3 5

Ammonia becarii tepida (CuSHMAN) A C C A. kawachiensis (CHIJI) C F A Buccella t上igida(CUSHMAN) F R R Bulimina aculeata (d'ORBIGNY) R Br必altnastriatula .(CUSHMAN) VR 一

Cibicides st. 一 R 一

Elphidium advena (CuSHMAN) C F F E. Icf. excavatum (TERQUEM) 一 F F E. hispidulum CuSHMAN R R C E. incertum (WILLIAMSON) R R A E. matagordanum (KORNiFELD) F R Globigerina bulloides (d'ORBIGNY) VR F "

G. falconensis BLOW F G. pachyderma (EHRENBFRG) F G. rubecens HOFKER R "

Glogigerinoides cyclostoma F (GALLOWAY & WISSLER)

G loboq uady，仇adutertrei (d'ORBIGNY) R "

G. cf. dutertrei (d'ORBIGNY) 一 C .

G. sp. VR 一

Globigerinita humilis (BRADY) C 一

λ，fasilina inaequalis CUSHMAN 一 R Sphaeroidine lla sp. R

Pollen assemblage studied by M AEDA: Pinus and Abies are predominant， and Tsuga and Sciadopitys follow them. Among the broad-leaved trees， Fagus， Quercus， Salix， Juglans，

Carpinus， Cor)ノルム Alnus， Ulmus， Zelkova and Praxinus are remarkable. Most of them

belong to the deciduous trees. Fagus and Quercus appear stably. Such facts indicate

that it was closely similar to the warm ten1perate deciduous fQrest.

，

/

Itami Terrace

一一一一一一一一一-Nω~ 吋(J)U) Q-Nω ゐ<.J10>吋∞σ1 0)

園田園田ーーーー・?圃園田

、

61

Sample number

Pinus

.' .園内.ceo

ーー --.- . -

B 1'1圃|田園田11'1;・11I 1'1 111田1:I圃1.I I

.. r-t

. . .，ー園・・・園田l圃圃・・ー

Abies

Tsuga

Taxodiaceae Sc/adopifys

Fagus

Quercus (ever green type)

、‘.，，aν nv vy

a'L

CM

Hu

so

uu

pνAu

mc

uぬ

Qんい

Ulmus-Zelkova

-・;・・'1・;.Alnus

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-・・-E 圃ー• ..ー

胴副 - - - ←一一一一.. 一ー司・・・ーー . -・・ーー' ーー- - ー一--一一一一 - ーー一一一一一司園田F・圃・・.--‘・・ -ーー -----_田.ーーー・園園曹司圃，・ーー - -唱圃-

.ー圃一一一一一ー一一一一一... p -・E 一ーーー

UUUU Eコ U 】'-J WUUUUUUUU

u 】 ~WUU~ <-I UU~lJU lJ】 "0

Eコー圃℃コ c::r 】】】 ] w ，コ

Betula Carpinus Corylus Jualans SaJix FraxinU5 Stvrax SODium

other trees

indeterminable •

grass

monolete

trilete

osmund

spore

Fig. 4 Pollen diagram of the Itami clay. Horizones of samp]es are given in Fig. 3. (by MAEDA)

、

，


As an indicator of the paleoclimatic condition， the con1bination of Abies， Tsuga and

Sciadopitys alTIOng conifers are considered to be suitable. Because， among the species of

Abies and Tsuga， only Abies firma s. et Z.， and Tsuga sieboldii CARR. can coexist with Sciadopitys verticillata S. et Z.， and they are now living in the lower mountain lands of 300-1，000 m high in the Kinki area. 80 the climate of the Itami age was probably some圃

what cooler than the present. This is also supported by the fact that the pollen grains of

deciduous trees are superior to those of evergreen trees. As the detai1s have been already

reported by MAEDA (1970)， only a typical pollen diagram is shown in Fig. 4.

KOKAWA descf，ibed the following plant remaines from Loc. 2: Sciadopitys verticillata

S. et Z.， Chamaecyparis obtusa ENDL.， Juniperus conferta PARLA.， Quercus sp.， Paliurus

sp.，λ4elia sp.， Sapium sp.， Zanthoxylum sp・，Prunus sp.， and Styrax japonica S. et Z.

He infers that the climate of Itami age was similar to that of the present.

Itami gravel

The pol1en assemblage from Loc. 9 has been examined. An10ng the conifer trees，

Pinus， Picea and Tsuga are dominant， and Betula， Fraxinus etc. are found. Doubtless-

ly， it was cold in that age. The environment of bog can be inferred from the existence

of Salix， Alnus， Osmundastrum and fernery of monolate type.

According to KlGOSHI， the radiometric age of the wood fragment from the same locality

is more than 40，100 Y.B.P. (Gak 1808). The authors infer that thおplantroot had been

derived from older deposits.

The radiocarbone圃 datesof the sediments which are correlatable to the Itami gravel

have been reported from fol1o¥lving localities in the Kinki district. The Tomita gravel

comprising the lower terrace of the Takatsuki area (Fig. 6) has radiocarbone-date of

26，000士800Y.B.P. (Gak 154) by KIGOSHI (1百HARA& !(.IGOSHI" 1962). From the same

locality， MIKI (1948) also reported fol1owing fossil plants indicating cool climate. Abies

homolepis S. et Z.， Acer miyabei var. shibatai (NAKAI)， Betula groass S. et Z.， Carpinus

erosa BL.， Alnus japonica S. et IZ.， Styrax japonica S. et Z.， Styrax obassioides恥1IKI

Ostrya japonica SARG..， Vitis coignetiae PULL. Carnus kousa BUERG.

Beneath the Port Island， which is， a reclamation land ，constructed outside the Kobe

Port (Fig. 6)， fine alternations of sands and gravels intercalated with many peat seams

prevail overlain by the Holocene deposits. The peat obtained from -14.5 m below sea

bottom shows the radiocarbone-date of 22，900+460 Y.B.P. (N-950). Ac∞C∞Oωrding tω O

勘MAEDA，pollen an叫y"siおsof i託ti加n吋d比ate郎sthe c∞01】dclimate as shown by such species aωs Piμceα'

Abiたesム，Tsuga仏，Betωulμ'0， Fraxinus and Osmundastrum.

The peat of the same horizon obtained from about 300 m far from the above Iocality con-

tains abundant seeds of Menyanthes triforiata LINN.， which is a good indicator of the cold

cHmate. Radiocarbonかdateof it is 23，800+ 520 Y.B.1? (N-951).

Depen:ding upon above圃 rnentionedfacts， the Itami gravel is considered to be deposited

in the climate becoming colder from the Interstade of the Main Wurm time.

‘

ltami 1errace 63

Tectonic situation of the Itami basin

Although the Itami formation is exposed as a terrace in the Itami area， most of it is dis-

tributed beneath Osaka Bay and the Osaka Plain covered with the Holocene deposits as

shown in Fig. 6 tentatively.

The ltami clay bed gently inclines to the south and can be confirmed to be thickest

near the mouth of the R. Yodo by many drill cores in Osaka Bay. lt is limited by the

extension of the Itami fault to the west、 Tothe east， it is restricted by the barrier of the

伝二

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、¥

¥ ; 150

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-ーーーー

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f

U ノ

E ・1 -.;.，，， I

ーー一

/' 〆'

-一一一一一一ー一-一ー一一

/

~. 噌，.

/

Fig. 5 Gravity contour map of the Itami area. The contour interval is 0.2 milligaI. (After E. ABE， K. KATSURA and S. NISH1MURA.)

Kazuo HUZITA and Yasuo MAEDA 64

-35000'

O

M『4

τd

Z《広《

2oxHnH

GM

G

回一で、1ha---』

HFuv o

w

o

νn

135030'

ムム.U.. Uムムムふみふ.u

135020'

_} Port Island

350

ay Osaka

2 口関

5km 。13'5030' 135020'

The map showing the outline of the tectonic framework of the Itami area and its surroundings and the distribution of the Itami clay. 1. The area in which the marine Itami clay is d'I1stributed; 2. The area in whicll the Itamli clay is exposed as terrace deposits.

E

。唱。〉.E

SENRI Hlll

。ょιコの~ ..E a: Itami T. a:

.ト伺』

mwzmwmω

コ

匡ヨQu仰 rnarysediment

医ヨGraniticbasement

Fig. 6

、

Diagrammatic profile from Rokko to Senri Hil1 across the Itami basin.

uplifts of Senri and Uemachi Hills. Only Kawachi basin between Ikoma and Uemachi

uplifts and the Yodogawa depression might be invaded by sea water of that time.

doubt that the Itami clay corresponds to the Marine clay No. 12 (Ma 12) recognized at

the depth of 40 ln in the deep dril1 cores， OD-1， at Osaka Port， which is overlain

the Holocene Umeda formation (IKEBE et al.， 1970). Such a distribution of the Itami clay is remarkably in harmony with the tectonic

fF~n1ework of the Osaka basin. This fact explains the reason of the poor distribution of

the lower terrace in the Osaka basin except for the Itami area， but， at the same time， it

suggests the tectonical1y peculiar position of the Itami area. The Itami basin has been

formed suffering from violent Quaternary crustal movement named “Rokko

which is described in detail in this volume (HUZITA et al.， 1971).

As suggested in the gravity contour map (Fig. 5)， the Itami basin is a small tectonic

It is no

by

Movement"

Fig. 7

ltami Terrace 65

basin bounded by faults. It is fil1ed up with the Quaternary Osaka group which is made of

alternations of gravel， sand and clay beds. It lies between tilted fault blocks inclined to

opposite directions each other as shown in Fig. 7.

In the Early Pleistocene， this area had been a depressional sedimentary basin including

Senri area due to the undulatory deformation of basement， but the ti1ting movements of the Rokko and Senri blocks become distinct rapidly from the Middle Pleistocene. How-

ever， the Itami block sandwiched between two blocks ti1ted towards opposite directions

had been left in lower position near sea level opening to the south in spite of the rapid eleva-

tion of blocks of both sides. It could be easily transgressed in the Late Pleistocene (Fig. 6).

After the deposition of the Itami formation， the Itami block has been continuing to

tilte to the west shifting the river course of the R. Muko towards west， but at the same

time， it has been rising in the north and tilting sout白hwa訂rdstωo the cente釘:rof 08鈎akaB

which has been the strongly distorted depressional part， as well as Lake Biwa， in Southwest

Japan.

The next post帽 glacialtransgression could not reach to the Itami basin.

Significance of the Itami transgression

The opinions that an eustatic rise in sea level took place during an interstade within the

Wurm Glaciation about 30，000 years ago have been announced by many authors， such as

HOPKINS (1959)， FAIRBRIGE (1961)， CURRAY (1961， 1965)， MILLIMAN et EMERY (1968) etc.

HOPKINS (1967) has proposed the WoronZiofian transgression selected the type locality near

Point Woronzofin Alaska. Recently， GUILCHER (1969) and OKA (1970) have examined the

worldwide distribution of the marine deposits of this transgression.

However， the sea level of this interstade might not rise as high as present sea level，

so the sediments of this transgression are regarded to be mostly buried beneath the alluvial

plain. They are only exposed on lands which have undergone late Quaternary uplift.

Several examples of such localities are listed in' Table 5.

The marine deposits which may be regarded to relate to the Itami transgression have

been reported from 111 localities in Japan as summarized in Table 6 and Fig. 8. Most of

Locality

Itami (Japan)

Brunei (Borneo)

Jaren Plain (Norway)

Woronzof (Alaska)

Baja California (Mexico)

Lobitos (Peru)

Mombasa (Kenya)

Tanga terrace (Tanganyika)

Prince Olav (Antarctica)

Table 5.

I Radiocarbone-Altitude (m)l date

31.6

15-30

7-27

36

8

23

4.5--15.0

13-17

20

29，800-32，700

29，600

34，000

25，000-30，000

25.000

30.000

21.600-26，500

23，800-30.600

23，000-38，000

Reporter

HUZITA & MAEDA (1971)

KOKAWA (unpublished)

ANDERSEN (1965)

HOPKINS (1967)

RICHARDS (1967)

RICHARDS (1967)

HORI (unpublished)

ALEXANDER (1968)

YOSHIDA (1970)

、

66 Kazuo I:tUZITA and Yasuo MAEDA

them are of marine terraces occupying slightly higher level than alluvial plain. They

belong to“lower terrace" and do not exceed 40 m. Some of them such as Yasugi bed (6)

are below sea level. Such facts clearly indicate the effects of the recent crustal move-

ment.

No. in Fig. 8

2

3

4

5

6

7

8

9

10

11

25

125 130

3

。d

C:?4・2Iqt

〆

135 140 145

Fig. 8 Distribution of the marine beds correlatable to the Itami clay in Japan.

Table 6.

Thickness Altitude LocaHty Sediments C14 age Reporter I(m) (m)

Tokunoshima coral +1.5 24，400 MACHJDA et al. --2.0 & (unpublished)

Kikaijima calcareous sand +35.0 27，200 Mn & KIGOSHI (1966)

Shimabara I Ohe bed 9.0 i +11.0 25，900 Ariake group (1965)

Wakamatsu Yamaguchi mud 10.0 +20.0 33，000 KAMEYAMA (1968)

Yasuoka Yokono sand 3.0 +10.0 33，000 KAMEYAMA (1986)

Naka・1Ifni Yasugi bed 8.0 - 8.0 29，100 恥1IZONOet al. (1970)

29，800 HUZITA & MAEDA Itami Itami clay 12.0 +31.6 32，700 (1971)

Koromogaura Hekkai bed 10.0+ + 4.5 32，400 SAKABE (1971)

I Not0 Uji sheH bed 7.0 I +21.0 21，200 FUJII (1969)

Toi Coastal terrace deposits 1.0+ + 7.0 33，600 SEGAWA (1970)

Tomamae Tomamae terrace deposi ts 14.0 +30--35 28，600 YANO (1970)

•

ltami Terrace 67

Summary

1) The marine Itami clay forming the Itami terrace， northwest of Osaka City， yields

+ 3，300 radiocarbonかdatesof 29，800土l，200Y.B.p.by wood and of 32，700-2，500 Y.B.p.by shell.

2) Although the Itami clay is exposed on land reaching 30 m at the highest part in the

Itami area， most of it is hidden beneath the Osaka Plain or Osaka Bay covered with the

Holocene deposits. The distribution of it is distinctly controlled by the late Quaternary

tectonic framework of the Osaka basiIi.

3) The climate of the Itami clay was moderate， but it might be slightly cooler than the

present， whi1e that of the Itami gravel was cold indicating the lowering of temperature.

4) The Itami transgression is considered to correspond to the eustatic rI'se in sea level that

took place during the Interstade of the Wurm Galiation.

References

ALEXANDER， C.S. (1968): The marine terraces of the northeast coast of Tanganiyika. Zeitschrift fur Geomorphologie， Supp. 7， p. 133-154.

ANDERSON. B.G. (1965): The Quaternary of Norway， in the Quaternary voI. 1. New York.

Ariake Bay Research Group (1965): Quaternary system of the Ariake and the Shiranui Bay

areas， with special reference to the Ariake soft clay (in Japanese with EngIish abstract). The Associati'On for the Geological Collaboration in Japan， Monograph 11.

CURRAY， J.B. (1961): Late Quaternary sea level. Geol. 80c. Amer. Bull.， 72， p. 1707-1712. CURRA Y， J .B. (1965): Late Quaternary history， continental shelves of the United States. The

Quaternary of the United States， p. 723-735. FAIRBRIDGE， R.W. (1961): Eustatic changes in sea level. Physics and Chemistry of the Earth，

p. 99-185.

FUJII， S. (1969): C14 age of the three shell bearing beds indicating the high sea level (in J apanese). Earth Sci. (Chikyu-Kagaku). 23， p. 216-218.

Geographical Survey Institute (1965): Land condition map of the Osaka plain (1/25，000) and its explanation (in Japanese).

GUILCHER， A. (1969): Pleistocene and Holocene sea level changes. Earth-Sci Rev. 5， p. 79-97. HASEGAWA， K. & M. SUZUKI (1964): Explanatory text of the geological map of Goryokaku，

1/50，000 (in Japanese wi，th Engtish abstract). Geological Survey of Hokkaido.

Hokuriku Quaternary Reseach Group (1961): Quaternary deposits on the marine terrace of Hiradoko， Noto Peninsula， Central Japan (in Japanese with English abstract). Earth Sciences (Chiyku Kagaku)， No. 54， p. 1-19.

Hokuriku Quaternary Research Group (1963): Quatemary deposits in the vicinity of Himi， Toyama Pref. Central Japan (in Japanese with English abstract). Earth Sci. (Chikyu-Kagaku)， No. 69， p. 1-15.

HOPKINS， D.M. (1959): Cenozoic history of the Bering land bridge. Science， 129， p. 1519-1528. HOPKINS~ D.M. (1967): Quatemary marine transgression in Alaska. The Bering Land Bridge，

Stanford Univ. Press， p. 47-90. HORI， N. (1971): The raised coral reefs along the eastern coast of Kenya， East Mrica. Geo岨

graphicaI reports of Tokyo Metropolitan Univ. 5， (in preparation). HUZITA， K. (1966): Tectonic significance of Osaka Bay (in Japanese with English abstract)， Prof.

S. MATSUSHITA Memorial Volume， Kyoto Univ.， p. 133-142.

HUZITA， K. & Y. MAEDA (1966): Latest Quaternary deposits of the northwestern part of Osaka Plain (in Japanese with English abstract). Quaternary Research， 5， p. 19-27.


HUZITA， K. (1969): Tectonic development of Southwest Japan in the Quaternary Period. Jour.

Geosci.， Osaka City Univ.， 12， p. 53-72. HUZITA， K. & Y. MAEDA (1969): Latest Qauternary deposits in Osaka Bay (in Japanese with

English abstract). Quaternary Research. 8， p. 89-100. HUZITA， K. et al. (1971): Geology and geomorphology of the Rokko area， Kinki district，

Japan， with special reference to the Quaternary tectonics. Jour. Geosci.， Osaka City Univ.

14， p.71-124. IKEBE， N.， J. IWATsu & J. TAKENAKA (1970): Quaternary geology of Osaka with special reference

to land subsidence. Jour. Geosci.， Osaka City Univ.， 13， p. 39-98. ITIHARA， M. (1960): Some problems of the Quaternary sedimentaries in the Osaka and Akashi

areas. Jour. Geosci.， Osaka City Univ. 5， p. 13，.....，30.

ITIHARA， M. & K. KIGOSHI (1962): Radiocarbone dates of peat and fossil-woods found from

the Recent and terrace deposits in the neighbourhood of Osaka (in Japanese). Earth

Sciences (ChilくylトKagaku)，No. 58， p. 35-36. ITOIGAWA， J. & K. NAKAYAMA (1968): The molluscan fauna of the Hekkai formation， Takahama，

Aichi Pref.， Japan (in Japanese with English abstract). “Venus"， Japanese Jour.恥1alacologicaI

Soc.， 27， p. 62-75. KAMEYAMA， T. (1968): The Pleistocene formation of the Kalnmon district (in Japanese with

English abstract). Jour. GeoI. Soc. Japan， 74， p. 415-426. KOKAWA， S. (1959): Morphometry of Menyanthes seed remains in Japan. Jour. Polytechnics，

D. Osaka City Univ. 10， p. 45-63. KOKAWA， S. (1961): Dおtriburtionand phytostratigraphy of Menyanthes remains in Japan. Jour.

Biology， Osaka City Univ. 12， p. 123-151. MAEDA， Y. (1970): Palynological study of the Iatest Pleistocene marine clay in the Itami area，

Kinki， Japan. Jour. Geosci.， Osaka City Univ. 13， p. 99-112. MAEDA， Y. & K. HUZITA (1971): Marine geol'ogy of Osaka Bay. (in tr句 aration).

Mn， H. & K. Kloosm (1966): Radiocarbone dating of the ancient beach and coastal dune

deposits， Kikai Island， Amami (in Japanese). Earth Sciences (Chikyu Kagaku)， 82， p. 43-45. MI悶， S. (1948): Floral remains in Kinki and adjacent districts since the Pleistocene (in Japanese

with English abstract). Mineral and Geology， 9， p. 105-144. MILLIMAN， J.D. & K.O. EMERY (1968): Sea levels during the past 35，000 years. Science， 162，

p. 1121-1123. MrZUNO， A.， K. OsmMA & K. KIOOSHI (1970): C14 ages of subsurface Quaternary peat bed in

the Lake Nakかumi，San'in district (in Japanese). Earth Sciences (Chikyu-Kagaku)， 24，

p. 76-78. OKA， Y. (1963): The geomorphologicaI development of the north圃 westernOsaka Plain (in

Japanese with English abstract). Geogr. Rev. Japan， 36， p. 309-322. OKA， Y. (1970): Some problems on Late Pleistocene sea level (in Japanese with English abstract).

Geogr. Sci. 14， p. 11-21. RICHARDS， H. G. (1967): A summary of the marine Quaternary of the Pacific coast of North

and South AmerI'ca. Jour. Geosci. Osaka City Univ.， 10" p. 83-90. RICHMOND， G. M. (1970): Comparison of the Quaternary stratigraphy of the Alps and Rocky

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itamii lierrace - osaka city...

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