Early Cretaceous Freshwater Fish Fauna in Kyushu, Japan

Early Cretaceous Freshwater Fish Fauna in Kyushu,Japan 117
upper part consists of alternating black sandstone and black sandy shale along the
Murasaki River (Fig. 4). At Tokuriki, the basal part directly overlies Paleozoic
rocks with remarkable clinounconformity and the main part is composed of alternat
ing sandstone, conglomerate and black shale. The upper part is composed of
abundant sandstone, yellowish-brown on weathered surface, with thin black shale
and the upper end of the formation is unknown at Tokuriki. The molluscan fossil
Brotiopsis wakinoensis is abundant and Plicatounio naklongensis naktongensis is common.
Fish fossils are found in green-gray shale and yellowish-gray shale of three horizons in
the main part at Tokuriki (Fig. 5). Plant and molluscan fossils are found in the
lowest horizon of fish fossils. There is a conglomerate above the horizons of fish
fossils and tuffaceous sandstone becomes abundant above the conglomerate.
The Second Formation (the middle formation, W2) correlates to the Nyoraida
Formation. This formation is distributed west of Ishida and along the Murasaki
River. The thickness is 250-320 m. The conglomerate, 3 m in thickness at the
base of the formation conformably overlies the black shale of the top of the lower
formation at the bottom of the Murasaki River near Kawarabashi Bridge. The
Second Formation unconformably directly overlies Paleozoic rocks west of Ishida.
The Second Formation is characterized by abundant pyroclastic rock, green-gray
calcareous fine sandstone, and intercalating, nodule-bearing and thin siliceous shale
(Fig.4). Molluscan fossils of Brotiopsis kobayashii, Viviparus onogoensis and Sphaerium (?)
sp., and Ostracoda were found at Takatsuo in Kokura-minami-ku (Y. Ota and
Yabumoto, 1992). No fish fossils have been found in the Second Formation.
The Third Formation (the upper formation, W3) correlates to the Lower
Wakamiya Formation. This formation is mainly distributed in and around Yamada
Park, the former military arsenal, and is distributed in the limited area along the
Murasaki River and its branch, the Oma River. The thickness is about 350-450 m.
It is composed mainly of sandstone, with alternating sandstone and shale, siliceous
shale, tuffand others (Fig.4). Fish fossils are found in the well-laminated yellowishwhite
and reddish-brown slate at Minamigaoka (Fig. 6). Molluscan fossils, Viviparus
onogoensis and Nakamuranaia (?) sp. cf. N. chingshanensis are abundant and Brotiopsis
kobayashii are present. Conchostracan and plant fossils are found together with
numerous Ostracoda yielded with fish fossils.
The Fourth Formation (the uppermost formation, W4) correlates to the Upper
Wakamiya Formation. This formation is widely distributed in and around Yamada
Park. The thickness is some 250 m. The basal part consists of a conglomerate of
white chert and unconformably or conformably overlies the Third Formation. The
Fourth Formation is composed chiefly of sandstone and siliceous shale, with shale,
tuff, conglomerate and reddish purple sandstone (Fig.4). Molluscan fossils of
Viviparus onogoensis and Brotiopsis sp., gastropods, Ostracoda, conchostracan, and plant
fossils are found in the Fourth Formation. Fish fossils are abundant in this
formation (Fig. 7).