itamii lierrace - osaka city...
TRANSCRIPT
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N. HORI for their 0仔ersof unpublished data.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
悼.;I._ 1 ~~ 0 0 01 1 11
£ 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
,
"
d
60 Kazuo HUZITA and Yasuo MAEDA
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
ーーーー ー -ー一一
-・・-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)
、
,
62 Kazuo HUZITA and Yasuo 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
/ ¥ノー
~ヘ¥
¥
ヨ
•
¥
、¥
¥ ; 150
'---,
U
一
-ーーーー
..-
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.
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