The correlation undertaken i n the present work includes the areas from western Kyushu to the Chita Peninsula in Aichi Prefecture because i t i s in this area that lacustrine de- posits are well developed, yield the same or very similar kind of flora and elephants indicating the same or almost identical age have been reported therefrom. Another reason for including this extensive area into consideration is because marine deposits yielding a very similar fauna occur from subjacent deposits and all are situated above either Paleo- gene or pre-Tertiary rocks with significant unconformity. For the purpose of correlation the stratigraphic sequence of Ehime and Kagawa Prefectures are taken as the basis.
I n the surveyed area the lower Neogene deposits are those referable to the Tonosho
group which comprises two formations, the Ikisue in the lower and the Shikai in the
upper, both in contact with one another with conformity From the lower or Ikisue for-
mation which is a lagoonal facies with lignite beds with Cinnamomum Zanceolatum HEER,
Sasa f ras sp., Metasequoza distzcha MIKI, Q U ~ Y C U S sp. (ever -green). This formation lies
on the pre-Tertiar y rocks of granite, Ryoke complex and the Paleozoic with significant
unconformity and is thought to correspond to the Shiomachi Iacustrine deposits in the
Hiroshima Prefecture district, which has yielded Hemitrapa
,yoke
yamae (NATH
.)
MIKI ,
Nelumbo nucz
f
era GAER
T N
, Liquidambar f ormosana HANCE , and Metasequoia japonica
MIKI. This formation like the Ikisue is unconformable with the basement of granite and
Paleozoic rocks. Both are lacustrine to lagoonal in character, yield a flora indicating a
similar age, and are similarly superposed with deposits of marine sediments.
The Ge0log.y o,f Kagawa and Northern Ehime Pre,f'ectures 59 I n the present area the Shikai formation with Glycymerzs cf. crassa KURODA, Turrztella cf . s-hatazi NOMURA, T . oyaszo IDA, EUSPZYU mezsenszs (MAKIYAMA) , and many others of Cardium, Siratoria , Nassarzus, etc. , whereas the corresponding lower part of the Bihoku group in the Hiroshima district has yielded besides abundant smaller for aminif er s , a molluscan fauna quite similar to that of the Shikai formation. Mzogypszna and Operculzna occur in the lower part of the Bihoku group which is superposed on the Shiomachi formation with local unconformity. Whether the whole Shikai marine facies corresponds to both upper and lower parts of the Bihoku group is difficult to determine from the absence of paleontological evidence. However , from the viewpoint of marine transgression , regression and local geological history of the two areas compared, it is thought that they may nearly contemporaneous in age.
The Tonosho group also corresponds to the Iwaya formation in Awaji Island, which i s superjacent with unconformity upon the basement of granitic rocks and which yields Turritella kzzenszs YOKOYAMA, Trichlanzya hrrsuta (LAMARCK) , and many others yet in need of paleontological study. This formation commences with marine transgression, i s situated not far away, ends with marine regression, and may belong t o a position similar to that of the Bihoku group and Tonosho group already mentioned.
Correlatives of the Tonosho group are found in the vicinity of Lake Biwa in Shiga Prefecture where the Ayukawa group is developed. This group covers the basement of granitic rocks and the Paleozoic with significant unconformity, commences with transglession and ends with regression I t s fauna comprises Vzcar ya yokoyamaz TAKEYAMA, Vzcar yella baculum (YOKOYAMA) , Soktellzna mznoenszs YOKOYAMA, Turrztella s-hatazz NOMURA, Katelysza nakamuraz IKEBE and many others. Thus from paleontological evidence i t is clear that the Ayukawa group is nothing but a correlative of the Tonosho and Bihoku groups already mentioned.
This is also the same as the Fujiwara group in Nara Prefecture which shows similar stratigraphic relation with the basement and yields a fauna comprising such as Cardita szogamenszs NOMURA, Macoma optzva (YOKOYAMA), Nuculana kongzenszs OTUKA, Yoldza sagittarza YOKOYAMA, Cardzum oguraz OTUKA and other typical early Miocene mollusca
(pelecypoda as well as gastropoda) .
I n Kyoto Prefecture there is developed the Tsuzuki group which covers the basement of Paleozoic with remarkable unconformity , commences with marine transgression over a n eroded land surface and yields such marine molluscs as Protorotella yuantanzensis MAKIYAMA, Katelysza nakamuraz IKEBE, Turrztella s-hatazz NOMURA, besides others of the genera Anadara, Glycymerzs, Perzploma, Dosznza, etc.. All of the fossils known from this group are characteristic in the early to middle Miocene of Japan and are unknown from late Miocene deposits. From such evidence as well as stratigr aphical relationships i t is evident that this group can be considered a correlative of the Fujiwara, Ayukawa, Iwaya, Tonosho and Bihoku groups already mentioned.
I n Mie Prefecture where the Isshi group is developed, A K A K ~ (1960) has described such molluscs as, Turrztella s - hatazz NOMURA, Turrztella oyaszo IDA, Aczla yanagawaenszs NOMURA and ZINBO, Glycymerzs cisshuenszs MAKIYAMA, Euspzra mezsenszs (MAKIYAMA) besides many others. This group transgresses over the Ryoke granite of pre-Tertiary age and its top is marked by a significant unconformity, just as in the cases already mentioned.
Although the f acies and thickness may be different in the diff ex ent stratigraphical units already mentioned, this has nothing to do with the geological ages of the respective areas, which are all thought to range from early to middle Miocene and sediments of late Miocene age are considered to be missing because there are no fossils indicating such an age.
The Miocene sedimentar ies developed in the Chita Peninsula in Aichi Prefecture have
yielded such fossils as Venerzcardza orbzca YOKOYAMA, Perzploma yokoyarnaz MAKIYAMA,
Pallzolum peckhami (GABB.), Solemya tokunagaz YOKOYAMA and many others, all of which
60 M. Saito
are also typical in the early to middle Miocene deposits of Japan.
The similarity in the marine fauna of all of the stratigraphic units so far mentioned i s only to be expected because all belong to the same geological age. I t is also noteworthy that the stratigraphical relation with subjacent and super jacent units is remarkably similar, although the thickness of the respective ones may be somewhat different and even though lacustr ine deposits or lagoonal ones are developed according to areas, because a land must have existed at that time.
I t is only in Oita Pr ef ecture where corresponding marine sediments are not developed, and in place there can be found the Usa group which i s volcanic facies comprised of agglomerate, breccia, tuff and lava flows This is also another characteristic features of the early Miocene of Japan because even where marine facies predominate there are generally always accompanied volcanics which may be different in thickness and extension, but always accompany the first extensive marine transgression of the early Miocene in the Japanese islands.
In the Kagawa and Ehime areas the Tonosho group i s covered with unconformity by thick volcanics assigned to the Sanuki group in the former and the Ishizuchi group in the latter area. This same period of volcanic activity i s widespread from Kyushu to Osaka Prefecture, being represented as the Higashi -Shonai volcanics in Oita Prefecture i n Kyushu, and the Futagami group in Osaka Prefecture. In Kyushu the Higashi-Shonai com- prises t u f f , sand, silt and lava with intercalated plant remains consisting of late Miocene floras as Fagus ferruginea AIT., Liquzdamdar formosana HANCE, Q U ~ Y C U S pseudocastanea GOPPERT, Metasequoza dzstzcha MIKI and Juglans cznersa LINNE, which occur i n the Sanuki group, the Ishizuchi group, Futagami group. The volcanics of the Sanuki group consist of tuff, agglomerate and sanukitic lavas which also occur i n the Ishizuchi group.
The Futagami group comprises the same kind of volcanic ejecta.
The stratigraphic relationship of the four mentioned groups with subjacent and super
-
jacent units is quite similar being unconformable everywhere.
I n all of the areas treated with in the present correlation, the Pliocene sediments are characterized with lacustrine or lake deposits, but the development of those deposits is not the same everywhere. However, all of them are unconformable with the subjacent units and the details are as follows.
The Taman and Kawauchi formations in Kagawa Prefecture are lateral extensions of the Okamura and the Gunchu for mations in Ehime Prefecture and the four formations are designated as the Mitoyo group. This group is characterized with Metasequoia distzcha MIKI , Pseudotsuga japonzca SHIRASAWA , S~quoza sempervzrens ENDLICH, Cunnigghamza Konishzi HAY, Pterocarya multistrzata M IKI, Eur yale akashienszs MIKI, Trapa mammzlz f era MIKI, Palzur us nzpponicus MIKI, Q U ~ Y C ~ L S rubrozdea MIKI, Pzcea Korzbaz MIKI, Juglans megacznerea CHANEY , besides many other plants. This f lor a1 assemblage (so-called the Metasequoza flora) occurs from the Ajina formation in the Yamaguchi-Hiroshima districts, the Miki gravel in the Kobe area, the Awaji group in Awaji Island, the Moriyama for -
mation in Tokushima Pr ef ectur e , the Shobudani for mation in Wakayama Pr ef ectur e, the Koyozn formation in Osaka Prefecture, the upper part of the Yuhi formation in the vicinity of Biwa Lake i n Shiga Prefecture, the Shirakawaike formation in Nara Prefecture, i n the upper part of the Kuwana group in Mie Prefecture, the Mihama group in the Chita Peninsula in Aichi Prefecture and the lacustrine deposits in Nagoya in Aichi Prefecture. This horizon is also the one of Stegodon shodoenszs akashiensis (TAKAI) which occurs in the uppermost part of the Kuwana group and the Akashi formation, of Parastegodon sugzyamaz TOKUNAGA from the Kawauchi formation, and their discovery from the other mentioned units is expected.
Although the mentioned correspond with one another in their lake facies, floral as-
semblage, str atigraphical relationship with super jacent and sub jacent units, except for the
The Geolog:y o,f Kagawa and N o ~ t h e r n Ehime Pre,fectures 61 fact that the time range is different. I t is considered that the Higashiueda-, Handa-, and Takio formations in Oita Prefecture range from early to late Pliocene, the Yokkaichi group in Mie Prefecture, the Kuwana group in Mie Prefecture also range from early to late Pliocene. The Mihama group in the Chita Peninsula in Aichi Prefecture, the Uji group in Kyoto Pr ef ectur e , the Gunchu for mation in Ehime Prefecture, the Shimakumayama gravel in Osaka Prefecture, and the lower part of the Kobiwako group in Shiga Prefecture are considered to begin from middle Pliocene whereas the Jigokudani formation in Nara Prefecture is thought to be an early Pliocene deposit.
The position of the lower part of each of the stratigaphic sequences of the Pliocene lake deposits are thought to be different a s already mentioned from the succession of the floral assemblages, the lower being characterized with old types of plants as Lzquzdambar formosana HANCE, Fagus ferrugznea AITON and S t y r a x obasszozdes MIKI which do not accompany so called the Metasequoza flora. The upper palt of the Pliocene lake deposits is characterized with the occurrence of Metasequoza distzcha MIKI and its associated flora, which do not occur from the lower part. This is the basis for leaving gaps between the Pliocene and Miocene deposits in several of the areas.
So far as is certain, the Pliocene lake deposits are overlain with younger sediments by distinct unconformity extending from Chita Peninsula and Nagoya in Aichi Prefecture southwards to Mie Prefecture, and again reappear in Kagawa, Tokushima and Ehime Prefectures, whereas elsewhere in the areas correlated with one another no sharp line of demarcation occurs until a higher horizon.
The Yakeotoge gravels typically developed in Kagawa and Ehime Prefectures is also found in Tokushima Prefecture. The extension of this kind of deposits is the Kentoyama gravels in Mie Prefecture, the Rengeji gravels in Aich Prefecture, the Taketoyo gravels in Chita Peninsula and the Osatsu gravels in Shima Peninsula. I n the Nagoya area the Yakeotoge gravels are represented by the Shiroyama and Yagoto gravels which axe said to be separated from one another by an unco nformity. In the Nara, Biwa Lake, Osaka, Kyoto, Kobe, Yamaguchi-Hiroshima, Oita and western Kyushu areas the Pliocene lake deposits with Metasequoza flora are succeeded with marine facies and the Pleistocene lake facies, which are thought to correspond to the Yakeotoge gravels and its correlatives already mention- ed. This horizon is characterized with the occurrence of Stegodon orzentalzs OWEN, ElePhas namadzcus naumannz MAKIYAMA, marine shells among which Volachlamys yagurai (MAKIYAMA), Chlamys ha1zmc;nszs (MAKIYAMA) , large size and elongate forms of Ostrea gzgas THUMBERG associated with TraPezzum lzratum REEVE and others, and Palzurus nipponzcus MIKI and its associated flora. This shows that marine transgression during the early Pleistocene was local, that is to say only fringing and drowning of the coastal area took place in the early phase although this was later followed by more extensive flooding.
Although paleontological evidence is insufficient in horizons higher than the Yakeotoge
gravels and its correlatives, the differences in heights above sea -level, materials compr is-
ing the units, and stratigraphical relationships with younger and older stratigraphical
units served for correlating them, and the results are given in the correlation table
(Table 6). I n the younger horizons ElePhas namadzcus naumannz MAKIYAMA occurs
without the association of Stegodon orzentalzs OWEN, and may be considered as the
