radiolaria - Marum

Radiolaria 14 Bibliography - 1989
This paper focuses on the late early Jurassic radiolarian
assemblage of bedded cherts and siliceous mudstones in the Mt.
Norikuradake area, central Japan. Nine multi-segmented
nassellarians of the assemblage including two new species, are
described herein. They belong to the genera Hsuum, Parahsuum and
Parvicingula and are characterised by forms possessing features of
both Parahsuum and Hsuum, with also a form of Parvicingula having
small tests. The assemblage containing these taxa, recognisable in
various localities in Southwest Japan and North America, is regarded
as a fauna of the transitional period from early Jurassic to middle
Jurassic forms. This assumption is based on a consideration of the
morphology of its component species. On the basis of its
biostratigraphic position and faunal content, the assemblage is
probably to be dated to a certain time in the late Early to early Middle
Jurassic, at least including Toarcian time.
Iijima, A., Kakuwa, Y. & Matsuda, H. 1989.
Silicified wood from the Adoyama Chert, Kuzuh, central
Honshu, and its bearing on compaction and depositional
environment of radiolarian bedded chert. In: Siliceous
Deposits of the Tethys and Pacific Regions. (Hein, J.R. &
Obradovic, J., Eds.). Springer-Verlag, New York. pp. 151-
168.
Ishida, K. 1989. Analysis of mesoscopic deformation
structures in melange with special respect to the stages of
syn- and post- sedimentation -A case study in the Southern
Chichibu Terrane in eastern Shikoku, Southwest Japan.
Struct. Geol., J. Tect. Res. Groupe Japan, 34, 95-109.
Ishiga, H. 1989. Paleozoic and Mesozoic radiolarians
fossils from Japan (Paleozoic 1-3). Atlas of Japanese fossils,
66, 1-12. (in Japanese)
Ishiga, H., Sugata, Y., Funakoshi, N.,
Takeshita, H. & Tokuoka, T. 1989. Biostratigraphy
and structure of the Permian Maizuru Group in western part of
Okayama Prefecture, Southwest Japan with special reference
to acid volcanic rocks. Geol. Rep. Shimane Univ., 8, 61-71.
(in Japanese)
The Permian rocks in the Ibara and Bisei areas. western part of
Okayama Prefecture consist of sedimentary complex rock units,
comprising the Maizuru Group of the Maizuru Terrane and the rocks
of the Ultra-Tamba Terrane. The complex of the Maizuru Group in the
Ibara area is divided into the following 5 units (unit A. B. C. D and E in
apparently ascending order) on the basis of lithology. composition,
age and structure.
The unit A mainly consists of acid volcanic and volcaniclastic
rocks and intercalated with mudstones. sandstones and
conglomerates. The ophiolite occurs in mudstones of the unit A.
The unit B is composed chiefly of mudstone including blocks of
basic volcanic rocks accompanying bedded cherts.
The unit C is Yakuno ophiolite, mainly consists of metabasalts
(MORB-like tholeiite) with metagabbro and ultramafic rocks.
The unit D consists of basic volcanic rocks and intercalated
with bedded cherts and mudstones.
The unit E of the Ultra-Tanba Tarrane is composed of alternated
beds of sandstones and mudstones. which are strongly sheared. The
units E. F and K are discriminated in the Bisei area.
The unit F consists of acid volcanic and volcaniclastic rocks
and intercalating mudstones and sandstones. which corresponds to
those of the unit A in the Ibara area. The unit K is composed of the
Kurohagi Formation mainly of mudstones yielding late Middle
Permian radiolarians. The mudstone includes acid volcanic rocks, and
intruded by acidic dykes.
Based on the radiolarian biostratigraphy and above evidence
especially occurrence of acid volcanic rocks and ophioiitic breccias
in the Maizuru Terrane. it could be inferred that a rifted-ophilite
assemblage of Early Permian age and acid volcanic rocks of late
Middle Permian age represent a fragment of back arc basin and
island arc.
Isozaki, Y. & Nishimura, Y. 1989. Fusaki Formation,
Jurassic subduction-accretion complex on Ishigaki Island,
southern Ryukyus and its geologic implication to Late
Mesozoic convergent margin of East Asia. In: High-pressure
metamorphic belts and tectonics of the inner zone of
southwestern Japan. (Nishimura, Y. et al., Eds.), vol. 33.
- 33 -
Memoirs of the geological Society of Japan, pp. 259-275.
(in Japanese)
Present study on the weakly metamorphosed pre-Tertiary rocks
(Fusaki Formation) on Ishigaki Island, southern Ryukyus has brought
new information concerning their tectono-sedimentary history as
follows. 1 ) The weakly metamorphosed rocks form a sedimentary
complex of olistostromal aspect, mostly dominated by pebbly
mudstone. It contains abundant allochthonous blocks and lenses of
sandstone, mudstone, chert, limestone, and so on. 2 ) Microfossils
such as conodonts, radiolarians and smaller foraminifers were newly
found out, providing age assignment for the exotic blocks and
lenses. Namely, the olistostromal complex contains Permian
limestone, Permian ( + Pennsylvanian?) and Triassic bedded cherts
and Early Jurassic siliceous mudstone. 3) Sandstone sills and dykes
intruded into the allochthonous blocks, indicating that these chaotic
sedimentary rocks were mixed before the consolidation of coarsegrained
clastic rocks. Judging from these results, the weakly
metamorphosed rocks are inferred to be a subduction-related
sedimentary complex formed in trench environs during the Middle
Jurassic, and are best compared with the Jurassic complex in
Southwest Japan, which is interpreted as an ancient subductionaccretion
complex along the eastern margin of Jurassic Asia.
On the other hand, previous studies have revealed that high P/T
metamorphic rocks with 240-160 Ma K-Ar ages (Tomuru Formation)
tectonically overlie upon the Fusaki Formation, and that they are
correlated to the Sangun metamorphic rocks in Southwest Japan.
Thus the pair of the high P/T metamorphic, rocks and the weakly
metamorphosed olistostromal complex on Ishigaki Island, southern
Ryukyu Arc, is compared with that of the Sangun metamorphic rocks
and adjacent Jurassic olistostromal complex (liuga Group) in the
Inner Zone of Southwest Japan. In other words, the southern Ryukyu
Arc is regarded as a southwestern extension of the Inner Zone of
Southwest Japan. while the northern Ryukyu Arc is surely a
southwestern extension of the Outer Zone. It is suggested,
therefore, that the northern and southern Ryukyu Arcs are offset in
left-lateral manner along the Kerama Gap, and that the width of the
Outer Zone becomes considerably narrower south-westward on the
south of Ishigaki Island. Concerning the Jurassic complex along the
eastern margin of Asia, its lateral extension is probably traced from
the Nadanhada area on China/USSR border to west Philippines
(probably further to west Borneo) via Japanese Islands, and the
Jurassic complex on Island gives a missing link in this organic chain
between Southwest Japan and North Palawan. west Philippines. The
boundary thrust between the Jurassic complex and the overlying pre-
Jurassic orogenic complexes, newly designated as the Ishigaki-Kuga
Tectonic Line in this paper, can be also traced along this trend in
East Asia.
Isozaki, Y. & Tamura, H. 1989. Late Carboniferous and
Early Permian radiolarians from the Nagato tectonic zone and
their implication to geologic structure of the Inner Zone,
southwest Japan. In: High-pressure metamorphic belts and
tectonics of the inner zone of southwestern Japan.
(Nishimura, Y. et al., Eds.), vol. 33. Memoirs of the
geological Society of Japan, pp. 167-176. (in Japanese)
Ages of some undated sedimentary rocks in the Nagato
Tectonic Zone in the western Chugoku district, Southwest Japan,
were examined by virtue of radiolarian biostratigraphy. The newly
obtained microfossil data strongly support the recent understanding
that the Nagato Tectonic Zone is continuous with the Hida Marginal
Zone in central Japan, in conjunction with the occurrence of coeval
high P/T schist in both zones. Late Carboniferous radiolarians were
found out from an andesitic tuffaceous mudstone of a sedimentary
unit previously called "undated Paleozoic formation in the Dai area,
Mine City. Such kind of andesitic tuffaceous mudstone is not known
at all in the Chugoku district but in the Hida Marginal Zone. This unit
is newly designated as the Higashi-hirano Formation.
Early Permian radiolarians were found out from an
allochthonous block of bedded chert, which is contained in coarsegrained
clastic rocks called the Toyohigashi Group in the Toyogadake
area. Toyota-cho. Judging from the age and mode of occurrence of
the chert block. and the total lithologic- assemblage of the unit, this
group can be properly correlated with the Middle-Late Permian
accretionary complex of the Akiyoshi Belt, which is distributed not
merely in the east of the Nagato Tectonic Zone but also in the Hida
Marginal Zone.
Iturralde-Vinent, M.A. 1989. Role of ophiolites in the
geological structure of Cuba. Geotectonics, 23/4, 332-342.
Iwasaki, T., Sashida, K. & Igo, H. 1989. Mesozoic
strata of the Kitaaiki-Kawakami area in Minamisaku County,
Nagano prefecture, northwest Kanto mountains, central
Japan. J. geol. Soc. Japan, 95/10, 733-753. (in Japanese)